query: when do genetic changes to a population due to mutations become more common

pos: Mutation genes and thereby produce genetic diversity. Nonlethal mutations accumulate within the gene pool and increase the amount of genetic variation. The abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favorable" mutations may accumulate and result in adaptive changes. For example, a butterfly may produce offspring with new mutations. The majority of these mutations will have no effect; but one might change the color of one of the butterfly's offspring, making it harder (or easier) for predators to see. If this color change is advantageous, the chances of this butterfly's surviving

pos: Mutation genes and thereby produce genetic diversity. Nonlethal mutations accumulate within the gene pool and increase the amount of genetic variation. The abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favorable" mutations may accumulate and result in adaptive changes. For example, a butterfly may produce offspring with new mutations. The majority of these mutations will have no effect; but one might change the color of one of the butterfly's offspring, making it harder (or easier) for predators to see. If this color change is advantageous, the chances of this butterfly's surviving

neg: Gene The genetic variation in relative frequencies of different alleles in a population is due to both natural selection and genetic drift. The wild-type allele is not necessarily the ancestor of less common alleles, nor is it necessarily fitter. Most mutations within genes are neutral, having no effect on the organism's phenotype (silent mutations). Some mutations do not change the amino acid sequence because multiple codons encode the same amino acid (synonymous mutations). Other mutations can be neutral if they lead to amino acid sequence changes, but the protein still functions similarly with the new amino acid (e.g. conservative mutations). Many

neg: Medical genetics of Jews There is evidence that the population bottleneck may have allowed deleterious alleles to become more prevalent in the population due to genetic drift. As a result, this group has been particularly intensively studied, so many mutations have been identified as common in Ashkenazim. Of these diseases, many also occur in other Jewish groups and in non-Jewish populations, although the specific mutation which causes the disease may vary between populations. For example, two different mutations in the glucocerebrosidase gene causes Gaucher's disease in Ashkenazim, which is their most common genetic disease, but only one of these mutations is found in non-Jewish

neg: Mutation and producing its own offspring are a little better, and over time the number of butterflies with this mutation may form a larger percentage of the population. Neutral mutations are defined as mutations whose effects do not influence the fitness of an individual. These can increase in frequency over time due to genetic drift. It is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness. Also, DNA repair mechanisms are able to mend most changes before they become permanent mutations, and many organisms have mechanisms for eliminating otherwise-permanently mutated somatic cells. Beneficial mutations can

neg: Introduction to evolution Introduction to evolution Evolution is the process of change in all forms of life over generations, and evolutionary biology is the study of how evolution occurs. Biological populations evolve through genetic changes that correspond to changes in the organisms' observable traits. Genetic changes include mutations, which are caused by damage or replication errors in organisms' DNA. As the genetic variation of a population drifts randomly over generations, natural selection gradually leads traits to become more or less common based on the relative reproductive success of organisms with those traits. The age of the Earth is about 4.54 billion years. The

neg: Genetic divergence Genetic divergence Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes (mutations) through time, often after the populations have become reproductively isolated for some period of time. In some cases, subpopulations living in ecologically distinct peripheral environments can exhibit genetic divergence from the remainder of a population, especially where the range of a population is very large (see parapatric speciation). The genetic differences among divergent populations can involve silent mutations (that have no effect on the phenotype) or give rise to significant morphological and/or physiological changes. Genetic divergence will always

neg: Genetic divergence divergence, and subsequently reproductive isolation, are the outcomes of multiple small mutations over evolutionary time. Genetic divergence Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes (mutations) through time, often after the populations have become reproductively isolated for some period of time. In some cases, subpopulations living in ecologically distinct peripheral environments can exhibit genetic divergence from the remainder of a population, especially where the range of a population is very large (see parapatric speciation). The genetic differences among divergent populations can involve silent mutations (that have no effect on

neg: Acute lymphoblastic leukemia These mutations produce a cell that divides more often, even in the absence of growth factors. Other genetic changes in B-cell ALL include changes to the number of chromosomes within the leukemic cells. Gaining at least five additional chromosomes, called high hyperdiploidy, occurs more commonly. Less often, chromosomes are lost, called hypodiploidy, which is associated with a poorer prognosis. Additional common genetic changes in B-cell ALL involve non-inherited mutations to "PAX5" and "IKZF1". In T-cell ALL, "LYL1", "TAL1", "TLX1", and "TLX3" rearrangements can occur. ALL results when enough of these genetic changes are present in a single lymphoblast. In childhood

neg: Sotos syndrome slightly greater than that of the general population. Mutations in the NSD1 gene cause Sotos syndrome. The NSD1 gene provides instructions for making a protein that is involved in normal growth and development. The function of this protein is unknown, however. In the Japanese population, the most common genetic change leading to Sotos syndrome deletes genetic material from the region of chromosome 5 containing the NSD1 gene. In other populations, small mutations within the NSD1 gene occur more frequently. Genetic changes involving the NSD1 gene prevent one copy of the gene from producing any functional protein. It is unclear how

neg: Neutral theory of molecular evolution (see synonymous or silent substitution). Such changes are presumed to have little or no biological effect. A second hypothesis of the neutral theory is that most evolutionary change is the result of genetic drift acting on neutral alleles, rather than for example genetic hitchhiking of a neutral allele due to genetic linkage with non-neutral alleles. After appearing by mutation, a neutral allele may become more common within the population via genetic drift. Usually, it will be lost, or in rare cases it may become fixed, meaning that the new allele becomes standard in the population. This stochastic process is assumed

neg: Genetic code to become more common in a population through natural selection. Viruses that use RNA as their genetic material have rapid mutation rates, which can be an advantage, since these viruses thereby evolve rapidly, and thus evade the immune system defensive responses. In large populations of asexually reproducing organisms, for example, "E. coli", multiple beneficial mutations may co-occur. This phenomenon is called clonal interference and causes competition among the mutations. Degeneracy is the redundancy of the genetic code. This term was given by Bernfield and Nirenberg. The genetic code has redundancy but no ambiguity (see the codon tables below for the

neg: Genetic purging changing environmental conditions often causes relevant genetic changes during inbreeding. Furthermore, if inbreeding is due to a reduction in population size, selection against new deleterious mutations can become less efficient, and this can induce additional fitness decline in the medium-long term. In addition, part of the inbreeding depression could not be due to deleterious alleles, but to an intrinsic advantage of being heterozygous compared to being homozygous for any available allele, which is known as overdominance. Inbreeding depression caused by overdominance cannot be purged, but seems to be a minor cause of overall inbreeding depression, although its actual importance is

neg: Adaptation record (the punctuated equilibrium theory). Genetic change occurs in a population when natural selection and mutations act on its genetic variability. The first pathways of enzyme-based metabolism may have been parts of purine nucleotide metabolism, with previous metabolic pathways being part of the ancient RNA world. By this means, the population adapts genetically to its circumstances. Genetic changes may result in visible structures, or may adjust physiological activity in a way that suits the habitat. Habitats and biota do frequently change. Therefore, it follows that the process of adaptation is never finally complete. Over time, it may happen that the

neg: Somatic evolution in cancer by a small number of underlying principles, despite the complexities of the disease. The authors describe how tumor progression proceeds via a process analogous to Darwinian evolution, where each genetic change confers a growth advantage to the cell. These genetic changes can be grouped into six "hallmarks", which drive a population of normal cells to become a cancer. The six hallmarks are: Genetic instability is defined as an "enabling characteristic" that facilitates the acquisition of other mutations due to defects in DNA repair. The hallmark "self-sufficiency in growth signals" describes the observation that tumor cells produce many of their own

neg: Introduction to genetics gene. These changes in DNA sequence are called mutations. Mutations produce new alleles of genes. Sometimes these changes stop the functioning of that gene or make it serve another advantageous function, such as the melanin genes discussed above. These mutations and their effects on the traits of organisms are one of the causes of evolution. A population of organisms evolves when an inherited trait becomes more common or less common over time. For instance, all the mice living on an island would be a single population of mice: some with white fur, some gray. If over generations, white mice became

neg: Frameshift mutation mechanisms present in a cell to ensure the correct transfer of genetic information during the process of DNA replication as well as during translation, mutations do occur; frameshift mutation is not the only type. There are at least two other types of recognized point mutations, specifically missense mutation and nonsense mutation. A frameshift mutation can drastically change the coding capacity (genetic information) of the message. Small insertions or deletions (those less than 20 base pairs) make up 24% of mutations that manifest in currently recognized genetic disease. Frameshift mutations are found to be more common in repeat regions of DNA.

neg: Autism or by rare multigene interactions of common genetic variants. Complexity arises due to interactions among multiple genes, the environment, and epigenetic factors which do not change DNA sequencing but are heritable and influence gene expression. Many genes have been associated with autism through sequencing the genomes of affected individuals and their parents. Studies of twins suggest that heritability is 0.7 for autism and as high as 0.9 for ASD, and siblings of those with autism are about 25 times more likely to be autistic than the general population. However, most of the mutations that increase autism risk have not been

neg: Evolution the frequencies of alleles within a population of interbreeding organisms, for example, the allele for black colour in a population of moths becoming more common. Mechanisms that can lead to changes in allele frequencies include natural selection, genetic drift, genetic hitchhiking, mutation and gene flow. Evolution by means of natural selection is the process by which traits that enhance survival and reproduction become more common in successive generations of a population. It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts: More offspring are produced than can possibly survive, and these conditions produce competition

neg: Stargardt disease investigation of the eye. Since the advent of genetic testing, the picture has become more complex. What was thought to be one disease is, in fact, probably at least three different diseases, each related to a different genetic change. Therefore it is currently a little confusing to define what Stargardt's disease is. It is certainly caused by defects in the ABCA4 gene, but whether changes to other genes such as PROM1 or ELOVL4, or missense mutations play a role remains to be seen. The carrier frequency in the general population of ABCA4 alleles is 5 to 10%. Different combinations of

neg: Cornelia de Lange syndrome behavior diminishes. There is evidence for some features of premature aging including the early development of Barrett’s esophagus, osteoporosis present in the teenage years, premature greying of hair and some changes to the skin of the face causing a more aged appearance compared to chronological age. The vast majority of cases are thought to be due to spontaneous genetic mutations. It can be associated with mutations affecting the cohesin complex. As at 2018, it was confirmed that 500 genetic mutations have been associated with the condition; occurring on 7 different genes. In around 30% of cases of CdLS the genetic

neg: Population genetics recombination. This leads to copy-number variation within a population. Duplications are a major source of raw material for evolving new genes. Other types of mutation occasionally create new genes from previously noncoding DNA. "Genetic drift" is a change in allele frequencies caused by random sampling. That is, the alleles in the offspring are a random sample of those in the parents. Genetic drift may cause gene variants to disappear completely, and thereby reduce genetic variability. In contrast to natural selection, which makes gene variants more common or less common depending on their reproductive success, the changes due to genetic drift

neg: Weak selection weak selection increases the impact of stochastic processes on the evolutionary dynamics of the trait being weakly selected. For example, genetic drift could cause a nearly neutral mutation to become the dominant allele in a population by wiping out the wild type. Weak selection is therefore also especially sensitive to the effects of population size. In smaller populations, a weakly selected mutation could proliferate due to stochastic processes such as genetic drift even more easily. Empirically, nonsynonymous substitutions have been reported to proliferate through weak selection in "Drosophila melanogaster" and "Arabidopsis". These non-neutral mutations are thought to have special significance

neg: Allopatric speciation alter a region's geography, resulting in the separation of a species population into isolated subpopulations. The vicariant populations then undergo genetic changes as they become subjected to different selective pressures, experience genetic drift, and accumulate different mutations in the separated populations gene pools. The barriers prevent the exchange of genetic information between the two populations leading to reproductive isolation. If the two populations come into contact they will be unable to reproduce—effectively speciating. Other isolating factors such as population dispersal leading to emigration can cause speciation (for instance, the dispersal and isolation of a species on an oceanic island) and

neg: Germline a genetic disorder, and of these, about 20% are due to newly arisen germline mutations. Germline In biology and genetics, the germline in a multicellular organism is the population of its bodily cells that are so differentiated or segregated that in the usual processes of reproduction they may pass on their genetic material to the progeny. As a rule this passing-on happens via a process of "sexual reproduction"; typically it is a process that includes systematic changes to the genetic material, changes that arise during recombination, meiosis and fertilization for example. However, there are many exceptions, including processes and concepts

neg: Tay–Sachs disease splice phase mutations, missense mutations, and other more complex patterns. Each of these mutations alters the gene's protein product (i.e., the enzyme), sometimes severely inhibiting its function. In recent years, population studies and pedigree analysis have shown how such mutations arise and spread within small founder populations. Initial research focused on several such founder populations: In the 1960s and early 1970s, when the biochemical basis of Tay–Sachs disease was first becoming known, no mutations had been sequenced directly for genetic diseases. Researchers of that era did not yet know how common polymorphisms would prove to be. The "Jewish Fur Trader

neg: Human mitochondrial molecular clock down along the matrilineal line, and therefore mutations passed down to sons are lost. Random genetic drift may also cause the loss of mutations. For these reasons, the actual mutation rate will not be equivalent to the mutation rate observed from a population sample. Population dynamics are believed to influence observed mutation rates. When a population is expanding, more germline mutations are preserved in the population. As a result, observed mutation rates tend to increase in an expanding population. When populations contract, as in a population bottleneck, more germline mutations are lost. Population bottlenecks thus tend to slow down observed

neg: G&T-Seq (e.g. Non-coding SNVs). While bulk sequencing of genome and transcriptome may allow one to associate a collection of genotypic features with mean expression patterns in a population of cells, it overlooks subtle or temporal differences between individual cells that may arise due to cell ecology. This presents an obstacle for researchers trying to pinpoint the genomic causes underlying transcript alterations, especially when compounded with tumour samples where heterogeneity is widespread and background genetic variation could confound relevant mutations. Conventional single cell sequencing, on the other hand, prevents one from making direct associations between mutations and changes in the transcriptome because

neg: Founder effect shows increased sensitivity to genetic drift, an increase in inbreeding, and relatively low genetic variation. In genetics, a founder mutation is a mutation that appears in the DNA of one or more individuals which are founders of a distinct population. Founder mutations initiate with changes that occur in the DNA and can be passed down to other generations. The mutation may occur in any organism that becomes a founder of the line of descendants containing that mutation, which could be as simple as a virus, a goat, or a more complex human. Founder mutations originate in long stretches of DNA

neg: Mutation mutations. Though relatively few mutations are advantageous, those that are play an important role in evolutionary changes. Like neutral mutations, weakly selected advantageous mutations can be lost due to random genetic drift, but strongly selected advantageous mutations are more likely to be fixed. Knowing the DFE of advantageous mutations may lead to increased ability to predict the evolutionary dynamics. Theoretical work on the DFE for advantageous mutations has been done by John H. Gillespie and H. Allen Orr. They proposed that the distribution for advantageous mutations should be exponential under a wide range of conditions, which, in general, has been

neg: Population size beneficial mutations. Small populations were noted to have an advantage in attaining full genomic complexity due to drift-driven phenotypic complexity. When deletion mutations were simulated, only the largest populations had any significant fitness advantage. These simulations demonstrate that smaller populations fix deleterious mutations by increased genetic drift. This advantage is likely limited by high rates of extinction. Larger populations evolve complexity through mutations that increase expression of particular genes; removal of deleterious alleles does not limit developing more complex genomes in the larger groups and a large number of insertion mutations that resulted in beneficial or non-functional elements within the

neg: Bateman's principle times of stable environment allows genetic variation to build up by random mutations and allow some individuals in a population to survive environmental change while strong constant selection offsets the effect and increases the risk of the entire population dying out during catastrophic environmental change due to less genetic variation, constant loss of genetic variation caused by sexual selection have been suggested as a factor contributing to higher extinction rates in more sexually dimorphic species besides the nutrient, immunity and other costs of the ornaments themselves. While the ornament cost risk would only be removed when the ornaments have been

neg: Evolution apart into two divergent populations with different sets of alleles. The neutral theory of molecular evolution proposed that most evolutionary changes are the result of the fixation of neutral mutations by genetic drift. Hence, in this model, most genetic changes in a population are the result of constant mutation pressure and genetic drift. This form of the neutral theory is now largely abandoned, since it does not seem to fit the genetic variation seen in nature. However, a more recent and better-supported version of this model is the nearly neutral theory, where a mutation that would be effectively neutral in

neg: Genetic distance mutations. It estimates the coancestry coefficient formula_24 which provides a measure of the genetic divergence by: Many other measures of genetic distance have been proposed with varying success. This distance assumes that genetic differences arise due to mutation and genetic drift, but this distance measure is known to give more reliable population trees than other distances particularly for microsatellite DNA data. It was specifically developed for microsatellite markers and is based on the stepwise-mutation model (SMM). formula_28 and formula_29 are the means of the allele sizes in population X and Y. This measure assumes that genetic differences arise due to

neg: Optimality model environmental change, and random effects such as genetic drift. Maximization requires both genetic and environmental stability, but real populations have discontinuous phenotypes and fluctuations in payoff. Strict optima may not be reachable due to genetic and environmental changes. Genetic factors that may limit the attainment of optimality include mutations and genetic linkage. Mutations can push populations away from the optimum. Additionally, beneficial and detrimental alleles sometimes stay together due to genetic linkage, inherently preventing an "optimal" state. This situation illustrates the broader perspective of genes as interacting together, as opposed to producing a combined result of independently arising characteristics. Environmental

neg: Genetic testing testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. Genetic testing identifies changes in chromosomes, genes, or proteins. The variety of genetic tests has expanded throughout the years. In the past, the main genetic tests searched for abnormal chromosome numbers and mutations that lead to rare, inherited disorders. Today, tests involve analyzing multiple genes to determine the risk of developing specific diseases or disorders, with the more common diseases consisting of heart disease and cancer. The results of a genetic test

neg: Behavior mutation more aggressive sex and there are genetic differences that back up this observation. A common explanation for this phenomenon is the higher testosterone levels in males. Testosterone levels have a direct effect on neurotransmitter functioning contributing to physical aggression. Mutations affecting neurotransmitters, as stated above, are the dominanting cause of changes in aggressive behaviour. Another contributors to the unequal male-female aggression ratio are the sex-linked gene mutations that affect only male behaviour, such as MAO-A mentioned above. These mutations could be the reason why males are nearly always more aggressive than females, although, testosterone levels are a much more feasible

neg: Genome evolution the code. The "copy-and-paste" mechanism works by making a genetic copy or copies of a specific region of DNA and inserting these copies elsewhere in the code. The most common transposable element in the human genome is the Alu sequence, which is present in the genome over one million times. Spontaneous mutations often occur which can cause various changes in the genome. Mutations can either change the identity of one or more nucleotides, or result in the addition or deletion of one or more nucleotide bases. Such changes can lead to a frameshift mutation, causing the entire code to be

neg: Creation–evolution controversy that genetic similarities between various animals imply a common ancestral relationship, and that scientists are coming to this interpretation only because they have preconceived notions that such shared relationships exist. Creationists also argue that genetic mutations are strong evidence against evolutionary theory because the mutations required for major changes to occur would almost certainly be detrimental. In biology, macroevolution refers to evolution above the species level while microevolution refers to changes within species. However, there is no fundamental distinction between these processes; small changes compound over time and eventually lead to speciation. Creationists argue that a finite number of discrete

neg: Albinism melanines and carotenoids. The latter are ingested in food and transformed into colour pigments by enzymes. Aberrations in this pigmentation are mostly caused by food deficiencies and usually do not have a genetic basis. Well-known examples are flamingos, which owe their distinct pink colour to the presence of red carotenoids in their natural food. When these carotenoids are in short supply, these birds appear white after the next moult. Mutations causing changes in carotenoid-based colour pigments are rare; melanine mutations occur much more frequently. Two types of melanin, eumelanin and phaeomelanin, are present in birds. In the skin and eyes,

neg: Cancer growth and reproduction. Tumor suppressor genes are genes that inhibit cell division and survival. Malignant transformation can occur through the formation of novel oncogenes, the inappropriate over-expression of normal oncogenes, or by the under-expression or disabling of tumor suppressor genes. Typically, changes in multiple genes are required to transform a normal cell into a cancer cell. Genetic changes can occur at different levels and by different mechanisms. The gain or loss of an entire chromosome can occur through errors in mitosis. More common are mutations, which are changes in the nucleotide sequence of genomic DNA. Large-scale mutations involve the deletion

neg: Evolution of sexual reproduction reproducing organisms. Muller described this occurrence by comparing the mutations that accumulate as a ratchet. Each mutation that arises in asexually reproducing organisms turns the ratchet once. The ratchet is unable to be rotated backwards, only forwards. The next mutation that occurs turns the ratchet once more. Additional mutations in a population continually turn the ratchet and the mutations, mostly deleterious, continually accumulate without recombination. These mutations are passed onto the next generation because the offspring are exact genetic clones of their parent. The genetic load of organisms and their populations will increase due to the addition of multiple deleterious

neg: Population genetics are not driven by environmental or adaptive pressures, and are equally likely to make an allele more common as less common. The effect of genetic drift is larger for alleles present in few copies than when an allele is present in many copies. The population genetics of genetic drift are described using either branching processes or a diffusion equation describing changes in allele frequency. These approaches are usually applied to the Wright-Fisher and Moran models of population genetics. Assuming genetic drift is the only evolutionary force acting on an allele, after t generations in many replicated populations, starting with allele

neg: Conservation genetics effective population size through equalization of family size all helps minimize inbreeding and its effects. Deleterious alleles arise through mutation, however certain recessive ones can become more prevalent due to inbreeding. Deleterious mutations that arise from inbreeding can be removed by purging, or natural selection. Populations raised in captivity with the intent of being reintroduced in the wild suffer from adaptations to captivity. Inbreeding depression, loss of genetic diversity, and genetic adaptation to captivity are disadvantageous in the wild, and many of these issues can be dealt with through the aforementioned techniques aimed at increasing heterozygosity. In addition creating a

neg: Nearly neutral theory of molecular evolution a mutation. When formula_11(completely neutral), formula_12, and when formula_13 (extremely deleterious), formula_14 decreases almost exponentially with formula_5. Mutations with formula_16 are called nearly neutral mutations. These mutations can fix in small-formula_5 populations through genetic drift. In large-formula_5 populations, these mutations are purged by selection. If nearly neutral mutations are common, then the proportion for which formula_19 is dependent on formula_20 The effect of nearly neutral mutations can depend on fluctuations in formula_10. Early work used a “shift model” in which formula_10 can vary between generations but the mean fitness of the population is reset to zero after fixation. This basically

neg: Benign tumor a visible tumor that is usually benign. Following promotion, progression may take place where more genetic mutations are acquired in a sub-population of tumor cells. Progression changes the benign tumor into a malignant tumor. A prominent and well studied example of this phenomenon is the tubular adenoma, a common type of colon polyp which is an important precursor to colon cancer. The cells in tubular adenomas, like most tumors which frequently progress to cancer, show certain abnormalities of cell maturation and appearance collectively known as dysplasia. These cellular abnormalities are not seen in benign tumors that rarely or never turn

neg: Grandmother hypothesis still carry a portion of their genes, it is still in the grandmother’s genetic interest to ensure those children survive to reproduction. The mismatch between the rates of degradation of somatic cells versus gametes in human females provides an unsolved paradox. Why do somatic cells decline at a slower rate and why do humans invest more in somatic longevity relative to other species? Since natural selection has a much stronger influence on younger generations, deleterious mutations during later life become harder to select out of the population. In female placentals, the number of ovarian oocytes is fixed during embryonic development,

neg: Pseudogene by population genetic modeling and also by genome analysis. According to evolutionary context, these pseudogenes will either be deleted or become so distinct from the parental genes so that they will no longer be identifiable. Relatively young pseudogenes can be recognized due to their sequence similarity. Various mutations (such as indels and nonsense mutations) can prevent a gene from being normally transcribed or translated, and thus the gene may become less- or non-functional or "deactivated". These are the same mechanisms by which non-processed genes become pseudogenes, but the difference in this case is that the gene was not duplicated before

neg: Genetic diversity human-caused population effects. A genetic bottleneck can occur when a population goes through a period of low number of individuals, resulting in a rapid decrease in genetic diversity. Even with an increase in population size, the genetic diversity often continues to be low if the entire species began with a small population, since beneficial mutations (see below) are rare, and the gene pool is limited by the small starting population. This is an important consideration in the area of conservation genetics, when working toward a rescued population or species that is genetically-healthy. Random mutations consistently generate genetic variation. A mutation

neg: Adaptation the speed and degree of the change. When the habitat changes, three main things may happen to a resident population: habitat tracking, genetic change or extinction. In fact, all three things may occur in sequence. Of these three effects only genetic change brings about adaptation. When a habitat changes, the resident population typically moves to more suitable places; this is the typical response of flying insects or oceanic organisms, which have wide (though not unlimited) opportunity for movement. This common response is called "habitat tracking". It is one explanation put forward for the periods of apparent stasis in the fossil

neg: Population bottleneck Population bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events (such as famines, earthquakes, floods, fires, disease, or droughts) or human activities (such as genocide). Such events can reduce the variation in the gene pool of a population; thereafter, a smaller population, with a smaller genetic diversity, remains to pass on genes to future generations of offspring through sexual reproduction. Genetic diversity remains lower, increasing only when gene flow with another population occurs or very slowly increasing with time as random mutations occur. As a consequence of such

neg: Genetic heterogeneity mutations that when combined contribute to the development of common diseases; (2) the accumulation of many different rare, individual mutations within the same gene that contribute to the development of the same common disease within different individuals; (3) the accumulation of many different rare, individual mutations within the same gene that contribute to the development of "different phenotypic variations" of the same common disease within different individuals; and (4) the development of the same common disease in different individuals through different mutations.<br> Increased understanding of the role of genetic heterogeneity and the mechanisms through which it produces common disease phenotypes

neg: Chemical biology a particular protein is conferred its cellular function. However, sometimes the folding process fails due to mutations in the genetic code and thus the amino acid sequence or due to changes in the cell environment (e.g. pH, temperature, reduction potential, etc.). Misfolding occurs more often in aged individuals or in cells exposed to a high degree of oxidative stress, but a fraction of all proteins misfold at some point even in the healthiest of cells. Normally when a protein does not fold correctly, molecular chaperones in the cell can encourage refolding back into its active form. When refolding is not

neg: Weismann barrier more sophisticated concepts of genetics in the early 20th century, is sometimes referred to as Weismannism. Some authors call Weismannist development (either preformistic or epigenetic) that in which there is a distinct germ line, differently of somatic embryogenesis. This type of development is correlated with the evolution of death of the somatic line. In plants, genetic changes in somatic lines can and do result in genetic changes in the germ lines, because the germ cells are produced by somatic cell lineages (vegetative meristems), which may be old enough (many years) to have accumulated multiple mutations since seed germination, some of

neg: Genetic diversity Small populations are more likely to experience the loss of diversity over time by random chance, which is called genetic drift. When an allele (variant of a gene) drifts to fixation, the other allele at the same locus is lost, resulting in a loss in genetic diversity. In small population sizes, inbreeding, or mating between individuals with similar genetic makeup, is more likely to occur, thus perpetuating more common alleles to the point of fixation, thus decreasing genetic diversity. Concerns about genetic diversity are therefore especially important with large mammals due to their small population size and high levels of

neg: Somatic evolution in cancer and those clones will tend to go extinct, but occasional selectively advantageous mutations arise that lead to clonal expansions. This theory predicts a unique genetic composition in each neoplasm due to the random process of mutations, genetic polymorphisms in the human population, and differences in the selection pressures of the neoplasm's microenvironment. Interventions are predicted to have varying results in different patients. What is more important, the theory predicts the emergence of resistant clones under the selective pressures of therapy. Since 1976, researchers have identified clonal expansions and genetic heterogeneity within many different types of neoplasms. There are multiple levels

neg: Saltation (biology) in the journal Nature in 2010 titled "Evolution: Revenge of the Hopeful Monster" reported that studies in stickleback populations in a British Columbia lake and bacteria populations in a Michigan lab have shown that large individual genetic changes can have vast effects on organisms "without dooming it to the evolutionary rubbish heap". According to the article "Single-gene changes that confer a large adaptive value do happen: they are not rare, they are not doomed and, when competing with small-effect mutations, they tend to win. But small-effect mutations still matter — a lot. They provide essential fine-tuning and sometimes pave the

neg: Molecular evolution mutation. Many genomic features have been ascribed to accumulation of nearly neutral detrimental mutations as a result of small effective population sizes. With a smaller effective population size, a larger variety of mutations will behave as if they are neutral due to inefficiency of selection. Selection occurs when organisms with greater fitness, i.e. greater ability to survive or reproduce, are favored in subsequent generations, thereby increasing the instance of underlying genetic variants in a population. Selection can be the product of natural selection, artificial selection, or sexual selection. Natural selection is any selective process that occurs due to the fitness

neg: Genetic isolate genetic isolation of the giraffe. The mitochondrial DNA of giraffe has been studied for mutations and loci substitutions between subspecies and suggests diversification around the Late Pleistocene, where geographic isolation was likely. The giraffe is a great example of how genetic isolation can happen in a number of ways and can lead to the diversification of a species.1 in 5 species become extinct every 4 years. The giraffe, "Giraffa camelopardalis", can be seen as a representation of the allopatric speciation that occurs due to genetic isolation of a population. Several clades of giraffe show differentiation within their mitochondrial DNA, varying

neg: Genetic drift theory of molecular evolution, which claims that most instances where a genetic change spreads across a population (although not necessarily changes in phenotypes) are caused by genetic drift acting on neutral mutations. The process of genetic drift can be illustrated using 20 marbles in a jar to represent 20 organisms in a population. Consider this jar of marbles as the starting population. Half of the marbles in the jar are red and half are blue, with each colour corresponding to a different allele of one gene in the population. In each new generation the organisms reproduce at random. To represent

neg: Human genetic variation differences—call the founder effect—from the overall populations where they originated; when these migrants settle new areas, their descendant population typically differs from their population of origin: different genes predominate and it is less genetically diverse. In humans, the main cause is genetic drift. Serial founder effects and past small population size (increasing the likelihood of genetic drift) may have had an important influence in neutral differences between populations. The second main cause of genetic variation is due to the high degree of neutrality of most mutations. A small, but significant number of genes appear to have undergone recent natural selection,

neg: Saccharomyces paradoxus purges recessive deleterious mutations that accumulated during clonal expansion, in a process known as "genome renewal". Post-zygotic isolation between strains of "Saccharomyces paradoxus" is commonly observed and could be either due to genetic divergence between populations or to chromosomal changes within populations. Like in other "Saccharomyces" species, heterothallism can be restored using standard genetic tools, to obtain stable haploid strains for experimental purposes. Saccharomyces paradoxus Saccharomyces paradoxus is a wild yeast and the closest known species to the baker's yeast "Saccharomyces cerevisiae". It is used in population genomics and phylogenetic studies to compare its wild characteristics to laboratory yeasts. "Saccharomyces

neg: Genetic hitchhiking similar behavior to the equation above, but with an effective population size that may have no relationship to the actual number of individuals in the population. Instead, the effective population size may depend on factors such as the recombination rate and the frequency and strength of beneficial mutations. The increase in variance between replicate populations due to drift is independent, whereas with draft it is autocorrelated, i.e. if an allele frequency goes up because of genetic drift, that contains no information about the next generation, whereas if it goes up because of genetic draft, it is more likely to go

neg: DNA mismatch repair expression of MLH1 or MSH2 in colorectal cancer. A field defect (field cancerization) is an area of epithelium that has been preconditioned by epigenetic or genetic changes, predisposing it towards development of cancer. As pointed out by Rubin " ...there is evidence that more than 80% of the somatic mutations found in mutator phenotype human colorectal tumors occur before the onset of terminal clonal expansion." Similarly, Vogelstein et al. point out that more than half of somatic mutations identified in tumors occurred in a pre-neoplastic phase (in a field defect), during growth of apparently normal cells. MLH1 deficiencies were common

neg: Terrigen Mist this. However, in the past, uncontrolled exposure to the Mists (due in part to Randac wishing for all the Inhumans to undergo Terrigen treatment or "Terrigenesis") mutated the majority of the Inhuman population into hideously deformed monsters. After centuries of eugenics and birth control, the Inhumans managed to mitigate the genetic damage and cultivated a more responsible use of the Terrigen Mists. The practice they developed was to let only genetically perfect specimens undergo the random mutations provoked by the Mists. Their theory was that genetic screening could avoid the risk of hideous and animal mutations in an individual. However,

neg: Nagwa Abdel Meguid the prize for the state of Scientific Excellence in Advanced Technology (2008). Meguid has contributed to the research and discovery of gene mutations causing common genetic disorders in the Egyptian population. These genetic disorders include phenylketonuria, Duchene muscular dystrophy, congenital sensorineural hearing loss and fragile X-syndrome. Meguid has developed methods to prevent certain genetic mutations, which includes heterozygous detection and prenatal diagnosis. She has diagnosed autosomal recessive disorders in Egyptians as a result of a high prevalence of consanguinity in the population. Meguid first discovered the prevalence of fragile X mutation among Egyptian males. The mutation occurred 0.9 per 1000

neg: Rett syndrome is caused by mutations in the gene MECP2 located on the X chromosome (which is involved in transcriptional silencing and epigenetic regulation of methylated DNA), and can arise sporadically or from germline mutations. In less than 10% of RTT cases, mutations in the genes CDKL5 or FOXG1 have also been found to resemble it. Rett syndrome is initially diagnosed by clinical observation, but the diagnosis is definitive when there is a genetic defect in the MECP2 gene. In some very rare cases, no known mutated gene can be found; possibly due to changes in MECP2 that are not identified by

neg: Prevention of Tay–Sachs disease techniques, and at very low cost. PCR techniques amplify a sample of DNA and then test genetic markers to identify actual mutations. Current PCR testing methods screen a panel of the most common mutations, although this leaves open a small probability of both false positive and false negative results. PCR testing is more effective when the ancestry of both parents is known, allowing for proper selection of genetic markers. Genetic counselors, working with couples that plan to conceive a child, assess risk factors based on ancestry to determine which testing methods are appropriate. Mutation analysis techniques have declined rapidly in

neg: Genetic disorder Genetic disorder A genetic disorder is a genetic problem caused by one or more abnormalities in the genome. Most genetic disorders are quite rare and affect one person in every several thousands or millions. Genetic disorders may be hereditary, meaning that they are passed down from the parents' genes. In other genetic disorders, defects may be caused by new mutations or changes to the DNA. In such cases, the defect will only be passed down if it occurs in the germline. Some types of recessive gene disorders confer an advantage in certain environments when only one copy of the gene

neg: Peripatric speciation experiences periods of geographic range expansion followed by periods of contraction. During the contraction phase, fragments of the population become isolated as small refugial populations on the periphery of the central population. Because of the large size and potentially greater genetic variation within the central population, mutations arise more readily. These mutations are left in the isolated peripheral populations, whereby, promoting reproductive isolation. Consequently, Brown suggested that during another expansion phase, the central population would overwhelm the peripheral populations, hindering speciation. However, if the species finds a specialized ecological niche, the two may coexist. The phylogenetic signature of this model

neg: Race and genetics reshuffling of genes through sexual reproduction. Variation is counteracted by natural selection and by genetic drift; note too the founder effect, when a small number of initial founders establish a population which hence starts with a correspondingly small degree of genetic variation. Epigenetic inheritance involves heritable changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the DNA sequence. Human phenotypes are highly polygenic (dependent on interaction by many genes) and are influenced by environment as well as by genetics. Nucleotide diversity is based on single mutations, single nucleotide polymorphisms (SNPs). The nucleotide diversity between humans

neg: Habitat fragmentation when inbreeding is associated with fitness reduction it is called inbreeding depression. Inbreeding becomes of increasing concern as the level of homozygosity increases, facilitating the expression of deleterious alleles that reduce the fitness. Habitat fragmentation can lead to inbreeding depression for many species due to reduced gene flow. Inbreeding depression is associated with conservation risks, like local extinction. Small populations are more susceptible to genetic drift. Genetic drift is random changes to the genetic make up of populations and always leads to reductions in genetic diversity. The smaller the population is, the more likely genetic drift will be a driving

neg: History of molecular evolution positions) based on the paradox first articulated by J. B. S. Haldane in 1937: the effect of deleterious mutations on the average fitness of a population depends only on the rate of mutations (not the degree of harm caused by each mutation) because more-harmful mutations are eliminated more quickly by natural selection, while less-harmful mutations remain in the population longer. H. J. Muller dubbed this "genetic load". Muller, motivated by his concern about the effects of radiation on human populations, argued that heterosis is primarily the result of deleterious homozygous recessive alleles, the effects of which are masked when separate

neg: Nucleic acid sequence are associated with inherited disorders. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person's chance of developing or passing on a genetic disorder. Several hundred genetic tests are currently in use, and more are being developed. In bioinformatics, a sequence alignment is a way of arranging the sequences of DNA, RNA, or protein to identify regions of similarity that may be due to functional, structural, or evolutionary relationships between the sequences. If two sequences in an alignment share a common ancestor, mismatches can be interpreted as point mutations and

neg: Cancer syndrome the correct preventative actions and surgery can be taken quicker. Regular breast screening is also recommended for women diagnosed with BRCA mutations, as well as that, recent studies show that men with increased risks of developing prostate cancer due to BRCA mutations can decrease their risk by taking aspirin. Aspirin is hugely beneficial in lowering cancer prevalence; however, it must be taken regularly over at least a five-year period to have any effect. Often genetic mutations are more common in certain ethnic groups, this is because a race can track their ancestors back to one geographic location, the mutated genes

neg: 23andMe 2018, the FDA approved another "de novo" application from the company, this one for a DTC test for three specific "BRCA" mutations that are the most common "BRCA" mutations in people of Ashkenazi descent; they are not however the most common "BRCA" mutations in the general population, and the test is only for three of the approximately 1,000 known mutations. These mutations increase the risk of breast and ovarian cancer in women, and the risk of breast and prostate cancer in men. 23andMe began offering direct-to-consumer genetic testing in November 2007. Customers provide a saliva testing sample that is partially

neg: Resistance Database Initiative to re-establish control over the virus. In well-resourced healthcare settings, when treatment fails a resistance test may be run to predict to which drugs the patient’s virus is resistant. The type of test in most common use is the genotype test, which detects mutations in the viral genetic code. This information is then typically interpreted using rules equating individual mutations with resistance against individual drugs. However, there are many different interpretation systems available that do not always agree, the systems only provide categorical results (resistant, sensitive or intermediate) and they do not necessarily relate well to how a patient will

neg: Genetic carrier about 1 of every 3,000 Caucasian newborns has CF, there are more than 900 known mutations of the gene that causes CF. Current tests look for the most common mutations. Genetic testing can be used to tell if a person carries one or more mutations of the CF gene and how many copies of each mutation. The test looks at a person’s DNA, which is taken from cells in a blood sample or from cells that are gently scraped from inside the mouth. The mutations screened by the test vary according to a person's ethnic group or by the occurrence

neg: Behavior mutation 35-minute time spans in bins of a 5-minute duration. The PPI measures the acoustic startle response, which is an exaggerated response to an unexpected stimulus. The acoustic startle is measured over a range of frequencies and amplitudes to calculate the average response. These tests allow us to detect abnormal behaviours and document them. In each generation, the genetic variation within a population increases due to accumulation of mutations and decreases in response to natural selection and genetic drift. Mutation accumulation occurs when mutations of small effect accumulate at certain loci, yielding a large phenotypic effect in the aggregate. Multiple genes

neg: Hypoxic ventilatory response ability to excel at mountaineering has shifted their culture around it. Tourism has become a driving force for the financial income of the Sherpa people. The Sherpa are able to make much more money acting as travel guides due to their local knowledge, and climbing ability. Genetic evidence suggests that the Tibetan peoples diverged from the larger Han Chinese population around 3,000 years ago. Given the significant mutations to the EPAS1 gene that contribute to the Tibetan resistance to altitude sickness, this suggests that the extreme evolutionary pressure on the Tibetan peoples has produced one of the fastest natural selection

neg: Genetic heterogeneity spectrum have high levels of genetic heterogeneity and result from multiple genetic pathways including single gene mutation disorders (such as Fragile X Syndrome), regional and submicroscopic variations in the number of gene copies (either heritable or de novo), rare and common genetic variants, and chromosomal aberrations. Mutations in ten different genes have been found to contribute to a heritable increased risk of breast cancer and other cancer syndromes. These genes, when functional, contribute to a pathway that serves to preserve genomic integrity. Mutations in BRCA1 and BRCA2 result in a high risk of both breast and ovarian cancers. Mutations in

neg: Genetic distance of domesticated animals are often investigated in order to determine which breeds should be protected to maintain genetic diversity. In the genome of an organism, each gene is located at a specific place called the locus for that gene. Allelic variations at these loci cause phenotypic variation within species (e.g. hair colour, eye colour). However, most alleles do not have an observable impact on the phenotype. Within a population new alleles generated by mutation either die out or spread throughout the population. When a population is split into different isolated populations (by either geographical or ecological factors), mutations that occur

neg: HCV genotypes indicates the 3.3% of the world population is infected by the HCV virus. Statistical records show that there are about 13 million HCV affected persons in china, 3.5 million affected persons in the United States, and about 10 million people are affected by HCV in Pakistan. In all cases, the viral genotype of the HCV stays the same, occasionally mutations do occur making the treatment more complex by targeting the changes in the genotype. Hepatitis C virus genotype is considered more common than the Hepatitis B virus infection contributing to more than a million cases annually and is considered one

neg: Osteopetrosis osteopetrosis are caused by genetic changes (mutations) in one of at least ten genes. There is nothing a parent can do before, during or after a pregnancy to cause osteopetrosis in a child. The genes associated with osteopetrosis are involved in the development and/or function of osteoclasts, cells that break down bone tissue when old bone is being replaced by new bone (bone remodeling). This process is necessary to keep bones strong and healthy. Mutations in these genes can lead to abnormal osteoclasts, or having too few osteoclasts. If this happens, old bone cannot be broken down as new bone

neg: Microevolution copies compared to the total number of gene alleles that share a particular form. Genetic drift is an evolutionary process which leads to changes in allele frequencies over time. It may cause gene variants to disappear completely, and thereby reduce genetic variability. In contrast to natural selection, which makes gene variants more common or less common depending on their reproductive success, the changes due to genetic drift are not driven by environmental or adaptive pressures, and may be beneficial, neutral, or detrimental to reproductive success. The effect of genetic drift is larger in small populations, and smaller in large populations.

neg: Natural selection mutations, the genetic variation at these sites is eliminated due to genetic drift. Natural selection reduces genetic variation by eliminating maladapted individuals, and consequently the mutations that caused the maladaptation. At the same time, new mutations occur, resulting in a mutation–selection balance. The exact outcome of the two processes depends both on the rate at which new mutations occur and on the strength of the natural selection, which is a function of how unfavourable the mutation proves to be. Genetic linkage occurs when the loci of two alleles are in close proximity on a chromosome. During the formation of gametes,

neg: History of molecular evolution more neutral. In this case, the faster rate of neutral evolution in proteins expected in small populations (due to genetic drift) is offset by longer generation times (and vice versa), but in large populations with short generation times, noncoding DNA evolves faster while protein evolution is retarded by selection (which is more significant than drift for large populations). Between then and the early 1990s, many studies of molecular evolution used a "shift model" in which the negative effect on the fitness of a population due to deleterious mutations shifts back to an original value when a mutation reaches fixation. In

neg: Somatic evolution in cancer majority of gene mutations are not recurrent types, and neither are the karyotypes. These analyses offer an explanation for the findings that there are no common mutations shared by most cancers. The state of a cell may be changed epigenetically, in addition to genetic alterations. The best-understood epigenetic alterations in tumors are the silencing or expression of genes by changes in the methylation of CG pairs of nucleotides in the promoter regions of the genes. These methylation patterns are copied to the new chromosomes when cells replicate their genomes and so methylation alterations are heritable and subject to natural selection.

neg: Genetic load its harm is felt for fewer generations. A slightly deleterious mutation may not stay in mutation-selection balance but may instead become fixed by genetic drift when its selection coefficient is less than one divided by the effective population size. In asexual populations, the stochastic accumulation of mutation load is called Muller's ratchet, and occurs in the absence of beneficial mutations, when after the most-fit genotype has been lost, it cannot be regained by genetic recombination. Deterministic accumulation of mutation load occurs in asexuals when the deleterious mutation rate exceeds one per replication. Sexually reproducing species are expected to have lower

neg: Evolution evolution as the change over time in this genetic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene. Variation disappears when a new allele reaches the point of fixation—when it either disappears from the population or replaces the ancestral allele entirely. Natural selection will only cause evolution if there is enough genetic variation in a population. Before the discovery of Mendelian genetics, one common hypothesis was blending inheritance. But with blending inheritance, genetic variance would be rapidly lost, making evolution by natural selection implausible. The Hardy–Weinberg principle provides the

neg: Speciation and color differences. During allopatric (from the ancient Greek "allos", "other" + "patrā", "fatherland") speciation, a population splits into two geographically isolated populations (for example, by habitat fragmentation due to geographical change such as mountain formation). The isolated populations then undergo genotypic or phenotypic divergence as: (a) they become subjected to dissimilar selective pressures; (b) they independently undergo genetic drift; (c) different mutations arise in the two populations. When the populations come back into contact, they have evolved such that they are reproductively isolated and are no longer capable of exchanging genes. Island genetics is the term associated with the

neg: Genetic monitoring for implementation of the Convention on Biological Diversity. Types of population changes that can be detected by genetic monitoring include population growth and decline, spread of pathogens, adaptation to environmental change, hybridization, introgression and habitat fragmentation events. Most of these changes are monitored using ‘neutral’ genetic markers (markers for which mutational changes do not change their adaptive fitness within a population). However markers showing adaptive responses to environmental change can be ‘non-neutral’ (e.g. mutational changes affect their relative fitness within a population). Two broad categories of genetic monitoring have been defined: Category I encompasses the use of genetic markers as

neg: Genetic load genetic loads. This is one hypothesis for the evolutionary advantage of sexual reproduction. Purging of deleterious mutations in sexual populations is facilitated by synergistic epistasis among deleterious mutations. High load can lead to a small population size, which in turn increases the accumulation of mutation load, culminating in extinction via mutational meltdown. The accumulation of deleterious mutations in humans has been of concern to many geneticists, including Hermann Joseph Muller, James F. Crow, Alexey Kondrashov, W. D. Hamilton, and Michael Lynch. New beneficial mutations create fitter genotypes than those previously present in the population. When load is calculated as the

neg: Muller's ratchet in an eventual accumulation of mutations known as genetic load. In theory, the genetic load carried by asexual populations eventually becomes so great that the population goes extinct. In sexual populations, the process of genetic recombination allows the genomes of the offspring to be different from the genomes of the parents. In particular, progeny (offspring) genomes with fewer mutations can be generated from more highly mutated parental genomes by putting together mutation-free portions of parental chromosomes. Among protists and prokaryotes, a plethora of supposedly asexual organisms exists. More and more are being shown to exchange genetic information through a variety

neg: Bacteria that may contain genes for various useful functions such as antibiotic resistance, metabolic capabilities, or various virulence factors. Bacteria genomes usually encode a few hundred to a few thousand genes. The genes in bacterial genomes are usually a single continuous stretch of DNA and although several different types of introns do exist in bacteria, these are much rarer than in eukaryotes. Bacteria, as asexual organisms, inherit an identical copy of the parent's genomes and are clonal. However, all bacteria can evolve by selection on changes to their genetic material DNA caused by genetic recombination or mutations. Mutations come from errors

neg: Genetic studies on Jews these communities by Sephardic Jewish progenitors. [...] When examining the presumed European component of these two communities, we demonstrate enrichment for Sephardic Jewish ancestry not only for these mutations, but also for other segments as well. [...] These findings are consistent with historical accounts of Jewish migration from the realms that comprise modern Spain and Portugal during the Age of Discovery. More importantly, they provide a rationale for the occurrence of mutations typically associated with the Jewish Diaspora in Latin American communities." Genetic studies on Jews Genetic studies on Jews are part of the population genetics discipline and are used

neg: Allopatric speciation many factors can alter a regions geography in substantial ways, resulting in the separation of a species population into isolated subpopulations. The vicariant populations then undergo genotypic or phenotypic divergence as: (a) they become subjected to different selective pressures, (b) they independently undergo genetic drift, and (c) different mutations arise in the gene pools of the populations. The extrinsic barriers prevent the exchange of genetic information between the two populations, inevitably leading to differentiation due to the ecologically different habitats they experience; selective pressure then invariably leads to complete reproductive isolation. Furthermore, a species' proclivity to remain in its ecological

neg: Adaptive mutation Adaptive mutation Adaptive mutation is a controversial evolutionary theory. It posits that mutations, or genetic changes, are much less random and more purposeful than traditional evolution. There have been a wide variety of experiments trying to prove (or disprove) the idea of adaptive mutation, at least in microorganisms. The most widely accepted theory of evolution states that organisms will diversify based on natural selection where changes caused by mutations improve the organism's chance of survival. Adaptive mutation states that rather than mutations and evolution being random, they are in response to specific stresses. In other words, the mutations that occur

neg: 1000 Genomes Project There is evidence that the genetic-basis of Type 1 Diabetes may have undergone positive selection. Few cases have been reported, where disease-causing mutations appear at the high frequencies supported by balanced selection. The most prominent example is mutations of the "G6PD" locus where, if homozygous G6PD enzyme deficiency and consequently Hemolytic anaemia results, but in the heterozygous state are partially protective against malaria. Other possible explanations for segregation of disease alleles at moderate or high frequencies include genetic drift and recent alterations towards positive selection due to environmental changes such as diet or genetic hitch-hiking. Genome-wide comparative analyses of different

neg: Wild type these wild-type mutations has also led to plants capable of growing in extremely arid environments, making more of the planet habitable than ever before. As more is understood about these genes, agriculture will continue to become a more efficient process, which will be relied upon to sustain a continually growing population. Amplification of advantageous genes allows the best traits in a population to be present at much higher percentages than normal, although this practice has been the subject of some ethical debate. These changes have also been the reason behind certain plants and animals being almost unrecognizable when compared to

neg: Evolutionary history of plants more male, with the ovules being expressed ectopically. These ovules initially performed the function of attracting pollinators, but sometime later, may have been integrated into the core flower. While environmental factors are significantly responsible for evolutionary change, they act merely as agents for natural selection. Change is inherently brought about via phenomena at the genetic level: mutations, chromosomal rearrangements, and epigenetic changes. While the general types of mutations hold true across the living world, in plants, some other mechanisms have been implicated as highly significant. Genome doubling is a relatively common occurrence in plant evolution and results in polyploidy, which