query: embryo refers to the stage of development between weeks

pos: Human embryogenesis Human embryogenesis Human embryogenesis refers to the development and formation of the human embryo. It is characterised by the process of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, human development entails growth from a one-celled zygote to an adult human being. Fertilisation occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences. Embryogenesis covers the first eight weeks

pos: Human embryogenesis of development; at the beginning of the ninth week the embryo is termed a fetus. Human embryology is the study of this development during the first eight weeks after fertilisation. The normal period of gestation (pregnancy) is nine months or 38 weeks. The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days. During this stage, the zygote begins to divide, in a process called cleavage. A blastocyst is then formed and implanted in the uterus. Embryogenesis continues with the next

pos: Development of the human body of the embryo that occurs during the early stages of development. In biological terms, human development entails growth from a one-celled zygote to an adult human being. Fertilisation occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of prenatal development commences. Embryogenesis covers the first eight weeks of development; at the beginning of the ninth week the embryo is termed a fetus. The germinal stage refers to the time from fertilization through the

neg: Development of the human body develops both into embryonic and extra-embryonic tissue, the latter forming the fetal membranes and the placenta. In humans, the embryo is referred to as a fetus in the later stages of prenatal development. The transition from embryo to fetus is arbitrarily defined as occurring 8 weeks after fertilization. In comparison to the embryo, the fetus has more recognizable external features and a set of progressively developing internal organs. A nearly identical process occurs in other species. Human embryogenesis refers to the development and formation of the human embryo. It is characterised by the process of cell division and cellular differentiation

neg: Pregnancy visible. Also during this time, there is development of structures important to the support of the embryo, including the placenta and umbilical cord. The placenta connects the developing embryo to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. The umbilical cord is the connecting cord from the embryo or fetus to the placenta. After about ten weeks of gestational age, the embryo becomes known as a fetus. At the beginning of the fetal stage, the risk of miscarriage decreases sharply. At this stage, a fetus is about 30 mm (1.2 inches)

neg: Juvenile (organism) fully mature and their development and growth stops. Their juveniles are larvae or nymphs. In vertebrates and some invertebrates (e.g. spiders), larval forms (e.g. tadpoles) are usually considered a development stage of their own, and "juvenile" refers to a post-larval stage that is not fully grown and not sexually mature. In amniotes and most plants, the embryo represents the larval stage. Here, a "juvenile" is an individual in the time between hatching/birth/germination and reaching maturity. Juvenile (organism) A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different

neg: Human embryogenesis be passed from the mother to the unborn child at any stage of its development. Hypoxia a condition of inadequate oxygen supply can be a serious consequence of a preterm or premature birth. Human embryogenesis Human embryogenesis refers to the development and formation of the human embryo. It is characterised by the process of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, human development entails growth from a one-celled zygote to an adult human being. Fertilisation occurs when the sperm cell successfully enters and fuses with an egg cell

neg: Prenatal nutrition based on physiological fetal development, which include blastogenesis, embryonic stage and fetal stage. Blastogenesis is the stage from fertilization to about 2 weeks. The fertilized egg or the zygote becomes a blastocyst where the outer layer and the inner cell mass differentiate to form placenta and the fetus respectively. Implantation occurs at this stage where the blastocyst becomes buried in the endometrium. Embryonic stage is approximately from 2 weeks to 8 weeks. It is also in this stage where the blastocyst develops into an embryo, where all major features of human are present and operational by the end of this

neg: Craniopagus parasiticus monozygotic twins start to develop as an embryo, but the embryo fails to completely split. When this happens, one embryo will dominate development, while the other's development is severely altered. The key difference between a parasitic twin and conjoined twins is that in parasitic twins, one twin, the parasite, stops development during gestation, whereas the other twin, the autosite, develops completely. In normal monozygotic twin development, one egg is fertilized by a single sperm. The egg will then completely split into two, normally at the two-cell stage. If the egg splits in the early blastocyst stage, two inner cell masses

neg: Prenatal nutrition stage. Fetal stage is from 9 weeks to term. During this period of time, the embryo develops rapidly and becomes a fetus. Pregnancy becomes visible at this stage. The pattern and amount of weight gain is closely associated with gestational stages. Additional energy is required during pregnancy due to the expansion of maternal tissues and stores in order to support fetal development. In the first trimester (blastogenesis and early embryonic stages), the mother experiences a minimal weight gain (approximately 0.5-2 kilograms), while the embryo weighs only 6 grams, which is approximately the weight of 6 raisins. In the second trimester

neg: Development of the human body and later fetus develops during gestation. Prenatal development starts with fertilization, the first stage in embryogenesis which continues in fetal development until birth. Fertilization occurs when the sperm successfully enters the ovum's membrane. The chromosomes of the sperm combine with those of the egg to form a single cell, called a zygote, and the germinal stage of embryogenesis commences. The germinal stage refers to the time from fertilization, through the development of the early embryo, up until implantation. The germinal stage is over at about 10 days of gestation. The zygote contains a full complement of genetic material and develops

neg: Face and neck development of the human embryo position and locates at the junction of the nasal cavity and the pharynx. The nasal septum grows as a downgrowth from the merged nasal prominences and fuses with the palatine process between the ninth and eleventh week. Finally, the superior, middle and inferior conchae develop the lateral wall of each nasal cavity. Face and neck development of the human embryo The face and neck development of the human embryo refers to the development of the structures from the third to eighth week that give rise to the future head and neck. They consist of three layers, the ectoderm, mesoderm and

neg: Plant embryogenesis name in eudicots because most plants from this group have two cotyledons, giving the embryo a heart shaped appearance. Between the cotyledons is where the shoot apical meristem lies. Stage IV, in the illustration above, indicates what the embryo looks like at this point in development. 5 indicates the position of the cotyledons. This stage is defined by the continued growth of the cotyledons and axis elongation. In addition, programmed cell death must occur during this stage. This is carried out throughout the entire growth process, like any other development. However, in the torpedo stage of development, parts of the

neg: Development of the human body and temporal changes in gene expression, cell growth and cellular differentiation. A nearly identical process occurs in other species, especially among chordates. A fetus is a stage in the human development considered to begin nine weeks after fertilization. In biological terms, however, prenatal development is a continuum, with many defining feature distinguishing an embryo from a fetus. A fetus is also characterized by the presence of all the major body organs, though they will not yet be fully developed and functional and some not yet situated in their final location. The fetus and embryo develop within the uterus, an organ

neg: Prenatal development of the egg by the sperm) and continues until the end of the 10th week of gestation (8th week by embryonic age). The period of two weeks from fertilization is also referred to as the germinal stage. The embryo spends the next few days traveling down the Fallopian tube. It starts out as a single cell zygote and then divides several times to form a ball of cells called a morula. Further cellular division is accompanied by the formation of a small cavity between the cells. This stage is called a blastocyst. Up to this point there is no growth

neg: Development of the human body into the embryo. Briefly, embryonic development have four stages: the morula stage, the blastula stage, the gastrula stage, and the neurula stage. Prior to implantation, the embryo remains in a protein shell, the zona pellucida, and undergoes a series of cell divisions, called mitosis. A week after fertilization the embryo still has not grown in size, but hatches from the zona pellucida and adheres to the lining of the mother's uterus. This induces a decidual reaction, wherein the uterine cells proliferate and surround the embryo thus causing it to become embedded within the uterine tissue. The embryo, meanwhile, proliferates and

neg: Implantation (human embryo) Implantation (human embryo) In humans, implantation is the stage of pregnancy at which the embryo adheres to the wall of the uterus. At this stage of prenatal development, the conceptus is called a blastocyst. It is by this adhesion that the embryo receives oxygen and nutrients from the mother to be able to grow. In humans, implantation of a fertilized ovum is most likely to occur around 9 days after ovulation, however this can range between 6 and 12 days. The reception-ready phase of the endometrium of the uterus is usually termed the "implantation window" and lasts about 4 days.

neg: Mammalian embryogenesis and marsupials undergoes the process of implantation, and forms the chorion with its chorionic villi, and later the placenta and umbilical cord, is also a difference from lower chordates. The difference between a mammalian embryo and an embryo of a lower chordate animal is evident starting from blastula stage. Due to that fact, the developing mammalian embryo at this stage is called a blastocyst, not a blastula, which is more generic term. There are also several other differences from embryogenesis in lower chordates. One such difference is that in mammalian embryos development of the central nervous system and especially the

neg: Holometabolism stage between larvae and adult. In 1883, John Lubbock revitalized Harvey's hypothesis and argued that the origin and evolution of holometabolan development can be explained by the precocious eclosion of the embryo. Hemimetabolan species, whose larvae look like the adult, have an embryo that completes all developmental stages (namely: "protopod", "polipod", and "oligopod" stages) inside the eggshell. Holometabolan species instead have vermiform larvae and a pupal stage after incomplete development and hatching. The debate continued through the twentieth century, with some authors (like Charles Pérez in 1902) claiming the precocious eclosion theory outlandish, Antonio Berlese reestablishing it as the leading

neg: Cephalic disorder caused by a disturbance that occurs very early in the development of the fetal nervous system. The human nervous system develops from a small, specialized plate of cells on the surface of the embryo. Early in development, this plate of cells forms the neural tube, a narrow sheath that closes between the third and fourth weeks of pregnancy to form the brain and spinal cord of the embryo. Four main processes are responsible for the development of the nervous system: cell proliferation, the process in which nerve cells divide to form new generations of cells; cell migration, the process in

neg: Magdalena Zernicka-Goetz her to discover that cell fate specification begins earlier than expected, an unexpected discovery but subsequently validated by her group and others. She found that this development of cell identity begins with heterogeneity in epigenetic regulation at the 4-cell stage that directs a molecular cascade establishing cell polarity, position and fate. Her recent development of systems permitting both mouse and human embryogenesis during implantation and early post-implantation stages "in vitro" allowed her to reveal that mouse and human embryo remodelling at implantation is done autonomously by the embryo. She uncovered the mechanism underlying embryo remodelling between the blastocyst and gastrula

neg: Foeticide certain federal officials, and other special cases. The law defines "child in utero" as "a member of the species "Homo sapiens", at any stage of development, who is carried in the womb." Of the 38 states that recognize fetal homicide, approximately two-thirds apply the principle throughout the period of pre-natal development, while one-third establish protection at some later stage, which varies from state to state. For example, California treats the killing of a fetus as homicide, but does not treat the killing of an embryo (prior to approximately eight weeks) as homicide, by construction of the California Supreme Court. Some

neg: Face and neck development of the human embryo Face and neck development of the human embryo The face and neck development of the human embryo refers to the development of the structures from the third to eighth week that give rise to the future head and neck. They consist of three layers, the ectoderm, mesoderm and endoderm, which from the mesenchyme (derived form the lateral plate mesoderm and paraxial mesoderm), neural crest and neural placodes (from the ectoderm). The paraxial mesoderm forms structures named somites and somitomeres that contribute to the development of the floor of the brain and voluntary muscles of the craniofacial region. The lateral plate

neg: Development of the human body development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days. During this stage, the zygote begins to divide, in a process called cleavage. A blastocyst is then formed and implanted in the uterus. Embryogenesis continues with the next stage of gastrulation, when the three germ layers of the embryo form in a process called histogenesis, and the processes of neurulation and organogenesis follow. In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. The entire process of embryogenesis involves coordinated spatial

neg: Prenatal development death rates, impaired lung and immune system development. Prenatal development Prenatal development () is the process in which an embryo and later fetus develops during gestation. Prenatal development starts with fertilization, the first stage in embryogenesis which continues in fetal development until birth. In human pregnancy, prenatal development, also known as antenatal development, is the development of the embryo following fertilization, and continued as fetal development. By the end of the tenth week of gestational age the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where many

neg: Prenatal development Prenatal development Prenatal development () is the process in which an embryo and later fetus develops during gestation. Prenatal development starts with fertilization, the first stage in embryogenesis which continues in fetal development until birth. In human pregnancy, prenatal development, also known as antenatal development, is the development of the embryo following fertilization, and continued as fetal development. By the end of the tenth week of gestational age the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where many organs become fully developed. This fetal period is

neg: Embryo drawing dissimilarity between hamster embryos and those of rabbits and dogs. Nevertheless, Bischoff's main argument was in reference to Haeckel's drawings of human embryos, for Haeckel is later accused of miscopying the dog embryo from him. Throughout Haeckel's time, criticism of his embryo drawings was often due in part to his critics' belief in his representations of embryological development as “crude schemata.” Michael Richardson and his colleagues in a July 1997 issue of "Anatomy and Embryology", demonstrated that Haeckel falsified his drawings in order to exaggerate the similarity of the phylotypic stage. In a March 2000 issue of "Natural History", Stephen

neg: Kangaroo to climb to the pouch and attach to a teat. In comparison, a human embryo at a similar stage of development would be about seven weeks old, and premature babies born at less than 23 weeks are usually not mature enough to survive. When the joey is born, it is about the size of a lima bean. The joey will usually stay in the pouch for about nine months (180–320 days for the Western Grey) before starting to leave the pouch for small periods of time. It is usually fed by its mother until reaching 18 months. The female kangaroo

neg: Preimplantation genetic diagnosis to this late stage of development limits the time to perform the genetic diagnosis, making it difficult to redo a second round of PCR or to rehybridize FISH probes before the embryos should be transferred back to the patient. Sampling of cumulus cells can be performed in addition to a sampling of polar bodies or cells from the embryo. Because of the molecular interactions between cumulus cells and the oocyte, gene expression profiling of cumulus cells can be performed to estimate oocyte quality and the efficiency of an ovarian hyperstimulation protocol, and may indirectly predict aneuploidy, embryo development and pregnancy

neg: Anorchia Anorchia Anorchia (also called anorchidism or anorchism) is a disorder of sex development in which a person with XY karyotype, which usually corresponds to male sex, is born without testes. Within a few weeks of fertilization, the embryo develops rudimentary gonads (testes), which produce hormones responsible for the development of the reproductive system. If the testes fail to develop within eight weeks, the baby will develop female genitalia (see Swyer syndrome). If the testes begin to develop but are lost or cease to function between eight and 10 weeks, the baby will have ambiguous genitalia when it is born. However,

neg: Neurula neurula stage embryo depending on the species. For example, in reptiles, extra-embryonic membrane tissues become distinct from the embryo. The neurula embryo has five regions of mesoderm that surround the neural tube. Anterior mesoderm develops into the head region, while posterior mesoderm develops into the trunk. Various molecules, including proteoglycans in the extracellular matrix, and genes, including Pax transcription factors, are essential for the development and closure of the neural tube in the neurula stage embryo. Neurulation is a process in vertebrate embryos at the neurula stage in which the neural tube is formed. There are two types of neurulation:

neg: Embryo transfer Embryo transfer Embryo transfer refers to a step in the process of assisted reproduction in which embryos are placed into the uterus of a female with the intent to establish a pregnancy. This technique (which is often used in connection with in vitro fertilization (IVF)), may be used in humans or in animals, in which situations the goals may vary. Embryo transfer can be done at day two or day three, or later in the blastocyst stage, which was first performed in 1984. Embryos can be either “fresh” from fertilized egg cells of the same menstrual cycle, or “frozen”, that

neg: Timeline of human prenatal development age: Weeks nr 34–38. 33–37 weeks old. Timeline of human prenatal development "Gestational age" is the time that has passed since the onset of the last menstruation, which generally or as standard occurs 2 weeks before the actual fertilization. "Embryonic age", in contrast measures the actual age of the embryo or fetus from the time of fertilization. Nevertheless, menstruation has historically been the only means of estimating embryonal/fetal age, and is still the presumed measure if not else specified. However, the actual duration between last menstruation and fertilization may in fact differ from the standard 2 weeks by several days.

neg: Development of the endocrine system medial and lateral anlage have fused together. At 12 weeks of gestation, the fetal thyroid is capable of storing iodine for the production of TRH, TSH, and free thyroid hormone. At 20 weeks, the fetus is able to implement feedback mechanisms for the production of thyroid hormones. During fetal development, T is the major thyroid hormone being produced while triiodothyronine (T) and its inactive derivative, reverse T, are not detected until the third trimester. Once the embryo reaches four weeks of gestation, the parathyroid glands begins to develop. The human embryo forms five sets of endoderm-lined pharyngeal pouches. The third

neg: Early stages of embryogenesis of tailless amphibians and on the temperature of the organism’s environment. For example, divisions in "R.pipiens" embryo occur once every hour, whereas in the "X.laevis embryo" – once every half hour. Higher temperature determines a faster division rate. The "R.pipiens" embryo reaches its 8-cell stage in 5.5 hours in the temperature of 18 degrees Celsius, and "X.laevis" does so in 4.5 hours in the same temperature. When the embryo is composed of over 10.000 blastomeres ("R.pipiens" – after 25 or 26 hours), the next stage of embryonic development begins – gastrulation, which lasts around 24 hours. The first visible stage of gastrulation is

neg: Endocrinology of reproduction normal embryonic development. Pregnancy-associated hormones such as hCG and sex steroids regulate numerous biological processes in the maternal system prior to and during pregnancy. The embryo orchestrates biological changes that occur in both the embryo and the mother. The embryo upregulates hCG, drives growth of the cell, and upregulates P4 production driving development. hCG and P4 direct changes in the mother to enable successful pregnancy (see below) via upregulation of specific hormones that act to direct both endocrinological and biological changes within the mother for successful pregnancy. The early embryo has 1–2 weeks in order to produce sufficient hCG in

neg: Berghia stephanieae able to locate their diet, sea anemones. The first detectable structures in the early veliger stage (5-10% of development), the larval shell and the ciliated velar lobes, appear at the same time as the first movements of the larvae (rotation around their anterior-posterior axes). Veliger stage (10-20% of development): The embryo can retract the velum into the shell and the eyes as well as the larval foot (propodium) appear. Late veliger stage (20-25% of development): The operculum is present and the foot becomes thicker and longer, the embryo hatches shortly prior to metamorphosis. Swimming is accomplished by ciliary beats of

neg: Beautiful demoiselle definitely the development with the final formation of the body shape until they hatch from the egg • the larval development of the hatched larva up to the formation of the winged imago The embryo in the egg can last between 20 days and one month. The larval development of the Blue-winged demoiselle takes into Middle Eastern waters, usually between six and nine weeks, mainly due to the preference of cooler waters, it is usually somewhat longer than that of the banded demoiselle. At the end of larval development, it comes to winter and the development until the following year

neg: Morphokinetics IVF Morphokinetics IVF Morphokinetics "(""‘morpho’’" form/shape "and ‘kinetics’" movement) refers to time specific morphological changes during embryo development providing dynamic information on a fertilized egg. The detailed information eases morphological selection of embryos with high implantation potential to be used in In-Vitro Fertilisation treatment. The traditional method for selection of embryos to be used for embryo transfer in fertility treatments such as IVF, involves assessing the morphology of a fertilized egg at crucial time points under a microscope. The incorporation of time lapse imaging tools in an incubator is a novel technology that allows images of embryo development to be captured

neg: Gestation Gestation Gestation is the period of development during the carrying of an embryo or fetus inside viviparous animals. It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time for example in a multiple birth. The time interval of a gestation is called the "gestation period". In human obstetrics, "gestational age" refers to the embryonic or fetal age plus two weeks. This is approximately the duration since the woman's last menstrual period (LMP) began. In mammals, pregnancy begins when a zygote (fertilized ovum) implants in the female's

neg: Early stages of embryogenesis of tailless amphibians layer, the mesoderm is the middle one, and the endoderm forms the inside layer. Only in the locations of the future body openings (the mouth and the anus), the endoderm remains in immediate contact with the ectoderm. In the next stage of development, which is known as neurulation, the embryo grows in length in the anterior-posterior axis. The differentiation of the germ layers also occurs. What is worth noticing is that cells communicate between one another, which means that the type of environment of specific cells implies their future roles in the development of the embryo. 1. Maleszewski, Marek."Ćwiczenia z

neg: Timeline of human prenatal development is already week three counting with gestational age. Furthermore, the number of the week is one more than the actual age of the embryo/fetus. For example, the embryo is 0 whole weeks old during the 1st week after fertilization. The following table summarizes the various expression systems during week number x of gestation. Gestational age: 2 weeks and 0 days until 2 weeks and 6 days old. 15–21 days from last menstruation. Embryonic age: Week nr 1. 0 (whole) weeks old. 1–7 days from fertilization. Gestational age: 3 weeks and 0 days until 3 weeks and 6 days old. 22–28

neg: Embryogenesis Embryogenesis Embryogenesis is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. Embryogenesis starts with the fertilization of the egg cell (ovum) by a sperm cell, (spermatozoon). Once fertilized, the ovum is referred to as a zygote, a single diploid cell. The zygote undergoes mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of a multicellular embryo. Although embryogenesis occurs in both animal and plant development, this article addresses the

neg: Embryo rescue medium that provides the proper nutrients to support survival and growth (Miyajima 2006). While the disinfestation and explant excision processes differ for these three techniques, many of the factors that contribute to the successful recovery of viable plants are similar. The main factors that influence success are; the time of culture, the composition of the medium, and temperature and light. Timing mainly refers to the maturation stage of the embryo before excision. The optimal time especially for the rescue of embryos involving incompatible crosses would be just prior to embryo abortion. Nevertheless, due to difficulties involved with the rearing of

neg: Obstetric ultrasonography Obstetric ultrasonography Obstetric ultrasonography is the use of medical ultrasonography in pregnancy, in which sound waves are used to create real-time visual images of the developing embryo or fetus in its mother's uterus (womb). The procedure is a standard part of prenatal care in many countries, as it can provide a variety of information about the health of the mother, the timing and progress of the pregnancy, and the health and development of the embryo or fetus. The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) recommends that pregnant women have routine obstetric ultrasounds between 18 weeks' and 22

neg: Embryo Embryo An embryo is an early stage of development of a multicellular diploid eukaryotic organism. In general, in organisms that reproduce sexually, an embryo develops from a zygote, the single cell resulting from the fertilization of the female egg cell by the male sperm cell. The zygote possesses half the DNA from each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. The result of this process is an embryo. In human pregnancy, a developing fetus is considered as an embryo until the ninth week, fertilization

neg: Circulatory system interstitial fluid back towards the heart for return to the cardiovascular system, by emptying into the lymphatic ducts. Its other main function is in the adaptive immune system. The development of the circulatory system starts with vasculogenesis in the embryo. The human arterial and venous systems develop from different areas in the embryo. The arterial system develops mainly from the aortic arches, six pairs of arches which develop on the upper part of the embryo. The venous system arises from three bilateral veins during weeks 4 – 8 of embryogenesis. Fetal circulation begins within the 8th week of development. Fetal

neg: Embryo abortion of some embryos can provide the remaining embryos with a greater share of maternal resources. This can also disturb the pregnancy, causing harm to the second embryo. Genetic strains which miscarry their embryos are the source of commercial seedless fruits. Abortion is the process of artificially (non-naturally) removing the embryo through deliberate pharmaceutical or surgical methods. Embryo An embryo is an early stage of development of a multicellular diploid eukaryotic organism. In general, in organisms that reproduce sexually, an embryo develops from a zygote, the single cell resulting from the fertilization of the female egg cell by the male

neg: Fetus Fetus A fetus or foetus (; plural fetuses, feti or foetuses) is the prenatal stage between the embryonic stage and birth . In human development the fetal stage begins from the ninth week after fertilisation (or eleventh week gestational age) and continues until birth. Prenatal development is a continuum, with no clear defining feature distinguishing an embryo from a fetus. However, a fetus is characterized by the presence of all the major body organs, though they will not yet be fully developed and functional and some not yet situated in their final anatomical location. The word "fetus" (plural "fetuses") is

neg: Fertilisation Upon gastrulation, which occurs around 16 days after fertilisation, the implanted blastocyst develops three germ layers, the endoderm, the ectoderm and the mesoderm, and the genetic code of the father becomes fully involved in the development of the embryo; later twinning is impossible. Additionally, interspecies hybrids survive only until gastrulation and cannot further develop. However, some human developmental biology literature refers to the "conceptus" and such medical literature refers to the "products of conception" as the post-implantation embryo and its surrounding membranes. The term "conception" is not usually used in scientific literature because of its variable definition and connotation. Insects

neg: Plant embryogenesis suspensor complex must be terminated. The suspensor complex is shortened because at this point in development most of the nutrition from the endosperm has been utilized, and there must be space for the mature embryo. After the suspensor complex is gone, the embryo is fully developed. Stage V, in the illustration above, indicates what the embryo looks like at this point in development. The second phase, or postembryonic development, involves the maturation of cells, which involves cell growth and the storage of macromolecules (such as oils, starches and proteins) required as a 'food and energy supply' during germination and seedling

neg: Hemichordate blastomeres also appear to give rise to these structures though the exact contribution varies from embryo to embryo. The macromeres give rise to the posterior larval ectoderm and the vegetal micromeres give rise to the internal endomesodermal tissues. Studies done on the potential of the embryo at different stages have shown that at both the two and four cell stage of development "P. flava" blastomeres can go on to give rise to a tornaria larvae, so fates of these embryonic cells don’t seem to be established till after this stage. Eggs of "S. kowalevskii" are oval in shape and become

neg: Morphokinetics IVF frequently. This together with softwares allows embryologists and clinicans to interpret the embryo development information captured and select embryos for transfer in IVF treatment. Research for an algorithm to select a single embryo that would lead to the best clinical pregnancy outcome is underway. Morphology of the embryo is studied in scientific research and often marked by stages. "For further details of the processes that occur within each stage, see Human embryogenesis." 1. Fertilization After the egg is fertilized by the sperm, a zygote (single diploid cell) is formed. At this stage, it should have two pronuclei, one of each

neg: Cleavage (embryo) cleavage. Two major types of meroblastic cleavage are discoidal and superficial. Differences exist between the cleavage in placental mammals and the cleavage in other animals. Mammals have a slow rate of division that is between 12 and 24 hours. These cellular divisions are asynchronous. Zygotic transcription starts at the two-, four-, or eight-cell stage. Cleavage is holoblastic and rotational. At the eight-cell stage, having undergone three cleavages the embryo goes through some changes. At this stage the cells begin to tightly adhere in a process known as compaction. A single cell can be removed from a pre-compaction eight- cell embryo

neg: Nervous system precursors, the migration of immature neurons from their birthplaces in the embryo to their final positions, outgrowth of axons from neurons and guidance of the motile growth cone through the embryo towards postsynaptic partners, the generation of synapses between these axons and their postsynaptic partners, and finally the lifelong changes in synapses which are thought to underlie learning and memory. All bilaterian animals at an early stage of development form a gastrula, which is polarized, with one end called the animal pole and the other the vegetal pole. The gastrula has the shape of a disk with three layers of

neg: Timeline of human prenatal development Timeline of human prenatal development "Gestational age" is the time that has passed since the onset of the last menstruation, which generally or as standard occurs 2 weeks before the actual fertilization. "Embryonic age", in contrast measures the actual age of the embryo or fetus from the time of fertilization. Nevertheless, menstruation has historically been the only means of estimating embryonal/fetal age, and is still the presumed measure if not else specified. However, the actual duration between last menstruation and fertilization may in fact differ from the standard 2 weeks by several days. Thus, the first week of embryonic age

neg: Endosperm family Poaceae) the endosperm persists to the mature seed stage as a storage tissue, in which case the seeds are called "albuminous" or "endospermous", and in others it is absorbed during embryo development (e.g., most members of the family Fabaceae, including the common bean, "Phaseolus vulgaris"), in which case the seeds are called "exalbuminous" or "cotyledonous" and the function of storage tissue is performed by enlarged cotyledons ("seed leaves"). In certain species (e.g. corn, "Zea mays"); the storage function is distributed between both endosperm and the embryo. Some mature endosperm tissue stores fats (e.g. castor bean, "Ricinus communis") and others

neg: Blastula Blastula The blastula (from Greek "βλαστός" (blastos), meaning "sprout") is a hollow sphere of cells, referred to as blastomeres, surrounding an inner fluid-filled cavity called the blastocoele formed during an early stage of embryonic development in animals. Embryo development begins with a sperm fertilizing an egg to become a zygote which undergoes many cleavages to develop into a ball of cells called a morula. Only when the blastocoele is formed does the early embryo become a blastula. The blastula precedes the formation of the gastrula in which the germ layers of the embryo form. A common feature of a vertebrate

neg: Neural plate have been major advances in the study of neurulation and the development and role of the neural plate in a growing embryo. The use of such techniques vary with the stage of development and overall research goals, but include such methods as cell labeling and grafting. The process of in situ hybridization (ISH) follows the labeling of a DNA or RNA sequence to serve as an antisense mRNA probe, complementary to a sequence of mRNA within the embryo. Labeling with a fluorescent dye or radioactive tag allows for the visualization of the probe and their location within the embryo. This

neg: Embryo rescue young embryos compared to those that have reached the autotrophic phase of development, embryos are normally allowed to develop in vivo as long as possible. While in general, two main types of basal media are the most commonly used for embryo rescue studies, i.e. Murashige and Skoog medium (MS) and Gamborg’s B-5 media (Bridgen, 1994), the composition of the medium will vary in terms of the concentrations of media supplements required. This will generally depend on the stage of development of the embryo. For instance, young embryos would require a complex medium with high sucrose concentrations, while more mature embryos

neg: Embryo a sphere or sheet of cells, also called blastomeres. In a placental mammal, an ovum is fertilized in a fallopian tube through which it travels into the uterus. An embryo is called a fetus at a more advanced stage of development and up until birth or hatching. In humans, this is from the eleventh week of gestation. However, animals which develop in eggs outside the mother's body, are usually referred to as embryos throughout development; e.g. one would refer to a chick embryo, not a "chick fetus", even at later stages. During gastrulation the cells of the blastula undergo coordinated

neg: Human tooth of dentin. Other cells in the pulp include fibroblasts, preodontoblasts, macrophages and T lymphocytes. The pulp is commonly called "the nerve" of the tooth. Tooth development is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, their development is largely the same as in humans. For human teeth to have a healthy oral environment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development. Primary teeth start to form in the development of the embryo between the sixth and eighth weeks, and

neg: Somatic embryogenesis is divided asymmetrically forming a small apical cell and large basal cell. The organizational pattern is formed in the globular stage and the embryo then transitions to the cotyledonary stage. Embryo development differs in monocots and dicots. Dicots pass through the globular, heart-shaped, and torpedo stages while monocots pass through globular, scuetellar, and coleoptilar stages. Many culture systems induce and maintain somatic embryogenesis by continuous exposure to 2,4-dichlorophenoxyacetic acid. Abscisic acid has been reported to induce somatic embryogenesis in seedlings. After callus formation, culturing on a low auxin or hormone free media will promote somatic embryo growth and root formation.

neg: Elysia chlorotica cleavage plane is at an oblique angle to the animal-vegetal axis of the egg. The result of this is that tiers of cells are produced, each tier lying in the furrows between cells of the tier below it. At the end of cleavage, the embryo forms a stereoblastula, meaning a blastula without a clear central cavity. "Elysia chlorotica" gastrulation is by epiboly: the ectoderm spreads to envelope the mesoderm and endoderm. After the embryo passes through a trochophore-like stage during development, it then hatches as a veliger larva. The veliger larva has a shell and ciliated velum. The larva uses

neg: Labia and form testes, which produce androgens (primarily male hormones), usually causing male genitals to be formed. Female genitals will usually be formed in the absence of significant androgen exposure. The genitals begin to develop after approximately 4 to 6 weeks of gestation. Initially, the external genitals develop the same way regardless of the sex of the embryo, and this period of development is called the "sexually indifferent" stage. The embroyo develops three distinct external genital structures: a genital tubercle; two urogenital folds, one on either side of the tubercle; and two labioscrotal swellings, each bounding one of the urogenital folds.

neg: Embryo culture the blastocyst stage confers a significant increase in live birth rate per embryo transfer, and there is no evidence of a difference between the groups in cumulative pregnancy rates. Transfer day 2 instead of day 3 after fertilization has no differences in live birth rate. Monozygotic twinning is not increased after blastocyst transfer compared with cleavage-stage embryo transfer. There are significantly higher odds of preterm birth (odds ratio 1.3) and congenital anomalies (odds ratio 1.3) among births from embryos cultured until the blastocyst stage compared with cleavage stage. Culture of embryos can either be performed in an artificial culture medium

neg: Blastula established which sets the foundation for further development and specification. Within the blastula, inner blastomeres are generally non-polar while epithelial cells demonstrate polarity. Mammalian embryos undergo compaction around the 8-cell stage where E-cadherins as well as alpha and beta catenins are expressed. This process makes a ball of embryonic cells which are capable of interacting, rather than a group of diffuse and undifferentiated cells. E-cadherin adhesion defines the apico-basal axis in the developing embryo and turns the embryo from an indistinct ball of to a more polarized phenotype which sets the stage for further development into a fully formed blastocyst.

neg: Mammary gland the invagination of cells within the placode into the mesenchyme, leading to a mammary anlage (biology). The primitive (stem) cells are detected in embryo and their numbers increase steadily during development Postnatally, the mammary ducts elongate into the mammary fat pad. Then, starting around four weeks of age, mammary ductal growth increases significantly with the ducts invading towards the lymph node. Terminal end buds, the highly proliferative structures found at the tips of the invading ducts, expand and increase greatly during this stage. This developmental period is characterized by the emergence of the terminal end buds and lasts until an

neg: Northern pike more stable the water, the greater the fitness of the pike. Mortality results from toxic concentrations of iron or rapid temperature changes, and adult abundance and the strength of the resulting year classes are not related. It is based upon two points of development: one during embryo stage between fertilization and closure of the blastopore, and the second between hatching and the termination of the alevin stage. The color of the sticky eggs is yellow to orange; the diameter is . The embryos are in length and able to swim after hatching, but stay on the bottom for some time.

neg: Embryonated and they most often refer to eggs. In Merriam-Webster the earliest known use of the term "embryonated" dates from 1687, while Oxford gives a reference dating from 1669. The term "embryonate" can be used as an adjective to mean "embryonated", or as a noun to mean "one containing an embryo" (e.g. "We selected only the embryonates and discarded the rest"). "Embryonate" can also be used as an intransitive verb meaning "to develop an embryo" (e.g. "In 2-4 weeks after deposition in soil, they embryonate if the soil conditions are suitable"). "De-embryonate" refers to the removal of embryos from seeds or

neg: Raillietina cesticillus are also often infected when they ingest infected beetles. A complete life cycle requires 2–4 weeks. One defining feature of the species during developmental stage is the occurrence of a single egg in each egg capsule. The development of an egg embryo to a mature cysticercoid in its intermediate host requires 28 days after infection, but fully mature cysticercoid takes about 31–34 days. Adults were found from chicken after 15 days of infection with mature cysticercoid, and the gravid segments can be obtained in the faeces from 27 to 112 days. Species of flour beetle "Tribolium" are particularly important as

neg: Somatic cell nuclear transfer after many mitotic divisions, this single cell forms a blastocyst (an early stage embryo with about 100 cells) with an identical genome to the original organism (i.e. a clone). Stem cells can then be obtained by the destruction of this clone embryo for use in therapeutic cloning or in the case of reproductive cloning the clone embryo is implanted into a host mother for further development and brought to term. Somatic cell nuclear transplantation has become a focus of study in stem cell research. The aim of carrying out this procedure is to obtain pluripotent cells from a cloned embryo.

neg: Embryo drawing most general, each embryo of a species departs more and more from a predetermined passage through the stages of other animals, and there is never a complete morphological similarity between an embryo and a lower adult. Von Baer's embryo drawings display that individual development proceeds from general features of the developing embryo in early stages through differentiation into special features specific to the species, establishing that linear evolution could not occur. Embryological development, in von Baer's mind, is a process of differentiation, "a movement from the more homogeneous and universal to the more heterogeneous and individual." Von Baer argues that

neg: Embryo age, or eleventh-week gestational age. After this time the embryo is referred to as a fetus. First attested in English in the mid-14c., the word "embryon" derives from Medieval Latin "embryo", itself from Greek ("embruon"), lit. "young one", which is the neuter of ("embruos"), lit. "growing in", from ἐν ("en"), "in" and βρύω ("bruō"), "swell, be full"; the proper Latinized form of the Greek term would be "embryum". In animals, the development of the zygote into an embryo proceeds through specific recognizable stages of blastula, gastrula, and organogenesis. The blastula stage typically features a fluid-filled cavity, the blastocoel, surrounded by

neg: Clearnose skate the embryo. The clearnose skate life cycle starts when a female deposits an egg. The embryo begins to enlarge as its cells divide. As division occurs, regionalization of the skate can be observed, with head and tail regions. Development continues with the formation of neural components, as well as spiracles and gill filaments. Other structures and organs continue to differentiate and grow, and finally the mottled pattern of the dorsal surface is developed. The embryos incubate within the egg case for approximately 12 weeks. Eventually, the embryo grows too large for the egg case, and will then break free by

neg: Prenatal development is usually due to major genetic mistakes or abnormalities in the developing embryo. During this critical period (most of the first trimester), the developing embryo is also susceptible to toxic exposures, such as: From the 10th week of gestation (8th week of development), the developing organism is called a fetus. All major structures are already formed in the fetus, but they continue to grow and develop. Since the precursors of all the major organs are created by this time, the fetal period is described both by organ and by a list of changes by weeks of gestational age. Because the

neg: Embryo drawing and comparison with other cases. Ultimately, His’ critical work in embryonic development comes with his production of a series of embryo drawings of increasing length and degree of development. His’ depiction of embryological development strongly differs from Haeckel's depiction, for His argues that the phylogenetic explanation of ontogenetic events is unnecessary. His argues that all ontogenetic events are the “mechanical” result of differential cell growth. His’ embryology is not explained in terms of ancestral history. The debate between Haeckel and His ultimately becomes fueled by the description of an embryo that Wilhelm Krause propels directly into the ongoing feud between

neg: Blighted ovum Blighted ovum A blighted ovum or anembryonic gestation (anembryonic pregnancy) is a pregnancy in which the embryo never develops or develops and is reabsorbed. It typically results in a miscarriage. In a normal pregnancy, an embryo would be visible on an ultrasound by six weeks after the woman's last menstrual period. Anembryonic gestation is one of the causes of miscarriage of a pregnancy. A blighted ovum or anembryonic gestation is characterized by a normal-appearing gestational sac, but the absence of an embryo. It likely occurs as a result of early embryonic death with continued development of the trophoblast. When small,

neg: Embryo culture Embryo culture Embryo culture is a component of "in vitro" fertilisation where in resultant embryos are allowed to grow for some time in an artificial medium . The duration of embryo culture can be varied, conferring different stages of embryogenesis at embryo transfer. The main stages at which embryo transfer is performed are cleavage stage (day 2 to 4 after co-incubation) or the blastocyst stage (day 5 or 6 after co-incubation). Embryos which reach the day 3 cell stage can be tested for chromosomal or specific genetic defects prior to possible transfer by preimplantation genetic diagnosis (PGD). Embryo culture until

neg: Midblastula expression are still unknown but being studied. Midblastula In developmental biology, midblastula or midblastula transition (MBT) occurs during the blastula stage of embryonic development. During this stage, the embryo is referred to as a blastula. The series of changes to the blastula that characterize the midblastula transition include activation of zygotic gene transcription, slowing of the cell cycle, increased asynchrony in cell division, and an increase in cell motility. Before the embryo undergoes the midblastula transition it is in a state of fast and constant replication of cells. The cell cycle is very short. The cells in the zygote are

neg: Midblastula Midblastula In developmental biology, midblastula or midblastula transition (MBT) occurs during the blastula stage of embryonic development. During this stage, the embryo is referred to as a blastula. The series of changes to the blastula that characterize the midblastula transition include activation of zygotic gene transcription, slowing of the cell cycle, increased asynchrony in cell division, and an increase in cell motility. Before the embryo undergoes the midblastula transition it is in a state of fast and constant replication of cells. The cell cycle is very short. The cells in the zygote are also replicating synchronously, always undergoing cell division

neg: Recapitulation theory as the recapitulation theory. Ontogeny is the growth (size change) and development (structure change) of an individual organism; phylogeny is the evolutionary history of a species. Haeckel claimed that the development of advanced species passes through stages represented by adult organisms of more primitive species. Otherwise put, each successive stage in the development of an individual represents one of the adult forms that appeared in its evolutionary history. For example, Haeckel proposed that the pharyngeal grooves between the pharyngeal arches in the neck of the human embryo not only roughly resembled gill slits of fish, but directly represented an adult

neg: Al-Alaq "ʻalaq" (singular ʻalaqah ) is "leech", "medicinal leech", "coagulated blood", "blood clot", or "the early stage of the embryo". "ʻAlaq" is also a derivative of "ʻalaqa" which means "attached and hanging to something." Professor Abdul Haleem mentions that ""ʻalaq"” can also mean anything that clings: a clot of blood, a leech, even a lump of mud. All these meanings involve the basic idea of clinging or sticking." The term "ʻalaqah" is the second stage of human prenatal development (sura Al-Mu’minoon 23: 12-14) which "descriptively encompasses the primary external and internal features" of the early embryo. The term "ʻalaqah" also occurs

neg: Chimera (genetics) of the embryo. Two- to eight-cell-stage embryos are competent for making chimeras, since at these stages of development, the cells in the embryos are not yet committed to give rise to any particular cell lineage, and could give rise to the inner cell mass or the trophectoderm. In the case where two diploid eight-cell-stage embryos are used to make a chimera, chimerism can be later found in the epiblast, primitive endoderm, and trophectoderm of the mouse blastocyst. It is possible to dissect the embryo at other stages so as to accordingly give rise to one lineage of cells from an

neg: Blastocyst vivo" fertilization for fertilizing an egg with sperm and implanting that embryo into a female’s womb. For many years the embryo was inserted into the uterus two to three days after fertilization. However at this stage of development it is very difficult to predict which embryos will develop best, and several embryos were typically implanted. Several implanted embryos increased the likelihood of a developing fetus but also led to the development of multiple fetuses. This was a major problem and drawback for using embryos to IVF. A recent breakthrough for "in vitro" fertilization is the use of blastocysts. A blastocyst

neg: Blastula and could guide vision based behavior in the "Xenopus". Blastula The blastula (from Greek "βλαστός" (blastos), meaning "sprout") is a hollow sphere of cells, referred to as blastomeres, surrounding an inner fluid-filled cavity called the blastocoele formed during an early stage of embryonic development in animals. Embryo development begins with a sperm fertilizing an egg to become a zygote which undergoes many cleavages to develop into a ball of cells called a morula. Only when the blastocoele is formed does the early embryo become a blastula. The blastula precedes the formation of the gastrula in which the germ layers of

neg: Somite form one after the other down the length of the embryo from the head to the tail, with each new somite forming on the caudal (tail) side of the previous one. The timing of the interval is not universal. Different species have different interval timing. In the chick embryo somites are formed every 90 minutes. In the mouse the interval is variable. For some species, the number of somites may be used to determine the stage of embryonic development more reliably than the number of hours post-fertilization because rate of development can be affected by temperature or other environmental factors.

neg: Chelodina expansa by rain. Turtles tend to select sites that have higher sun coverage to construct their nests. The selection of nest sites is often a long way from the waters edge and this is seen as a behavioural strategy to minimise the risk of nest flooding. Hatchlings are however exposed to a number of challenges during their travels to the water. and the incubation period is exceptionally long due to inherently slow embryonic development, averaging between 324 and 360 days. The development of the embryo also slows the process as it enters a two distinct diapause stages. The primary diapause stage

neg: Carnegie stages stages" comes from the Carnegie Institution of Washington. While the Carnegie stages provide a universal system for staging and comparing the embryonic development of most vertebrates, other systems are occasionally used for the common model organisms in developmental biology, such as the Hamburger–Hamilton stages in the chick. Days are approximate, and reflect the days since the last ovulation before pregnancy ("Postovulatory age"). Carnegie stage 1 is the unicellular embryo. This stage is divided into three substages. Primordial embryo. All the genetic material necessary for a new individual, along with some redundant chromosomes, are present within a single plasmalemma. Penetration of

neg: Embryo transfer Embryo transfer can be performed after various durations of embryo culture, conferring different stages in embryogenesis. The main stages at which embryo transfer is performed are cleavage stage (day 2 to 4 after co-incubation) or the blastocyst stage (day 5 or 6 after co-incubation). Embryos who reach the day 3 cell stage can be tested for chromosomal or specific genetic defects prior to possible transfer by preimplantation genetic diagnosis (PGD). Transferring at the blastocyst stage confers a significant increase in live birth rate per transfer, but also confers a decreased number of embryos available for transfer and embryo cryopreservation, so

neg: Neurula Neurula A neurula is a vertebrate embryo at the early stage of development in which neurulation occurs. The neurula stage is preceded by the gastrula stage; consequentially, neurulation is preceded by gastrulation. Neurulation marks the beginning of the process of organogenesis. Mice, chicks, and frogs are common experimental models for studying the neurula. Depending on the species, embryos reach the neurula stage at different time points and spend a varying amount of time in this stage. For oviparous organisms, incubation temperature also affects the length of neurulation. In addition to development of the neural tube, other processes occur in a

neg: Fate mapping may not accommodate single-cell resolution studies at later stages of development, since successive cell divisions will yield smaller cells (until the embryo develops into a larval form that can eat, and thereby grow larger). Additionally, the cell or cell population of interest must be superficial, since the agar chip with the dye must be placed on the surface of the embryo. The information Vogt gathered from his tracing experiments of distinct cells and populations of cells in "Xenopus" was then pooled to construct a fate map. The map was a representation of an early-stage embryo (such as a blastula) that

neg: Bareback (sex) vaginally or anally, and an increased risk of pregnancy. In addition to sexually transmitted infections, mechanical trauma are the same as in anal sex. Unprotected anal sex is a risk factor for formation of antisperm antibodies (ASA) in the recipient. In some people, ASA may cause autoimmune infertility. Antisperm antibodies impair fertilization, negatively affect the implantation process and impair growth and development of the embryo. Bareback (sex) Bareback sex is physical sexual activity, especially sexual penetration, without the use of a condom. It most commonly refers to anal sex between men who have sex with men without the use of

neg: Frilled shark to fifteen, with an average of six. Females ovulate eggs into the uterus about once every two weeks; vitellogenesis (yolk formation) and the growth of new ovarian eggs halt during pregnancy, apparently due to insufficient space inside the body cavity. Newly ovulated eggs and early-stage embryos are enclosed in a thin, ellipsoid, golden-brown capsule. When the embryo is long, the head is pointed when seen from above or below, the jaws are barely developed, the external gills have begun to appear, and all the fins are present. The egg capsule is shed when the embryo grows to long, and is

neg: Developmental psychology has some weaknesses, developmental psychologists rarely rely on one study or even one method to reach conclusions by finding consistent evidence from as many converging sources as possible. Prenatal development is of interest to psychologists investigating the context of early psychological development. The whole prenatal development involves three main stages: germinal stage, embryonic stage and fetal stage. Germinal stage begins at conception until 2 weeks; embryonic stage means the development from 2 weeks to 8 weeks; fetal stage represents 9 weeks until birth of the baby. The senses develop in the womb itself: a fetus can both see and hear

neg: Chimera (genetics) Between the stages of fertilization of the egg and the implantation of a blastocyst into the uterus, different parts of the mouse embryo retain the ability to give rise to a variety of cell lineages. Once the embryo has reached the blastocyst stage, it is composed of several parts, mainly the trophectoderm, the inner cell mass, and the primitive endoderm. Each of these parts of the blastocyst gives rise to different parts of the embryo; the inner cell mass gives rise to the embryo proper, while the trophectoderm and primitive endoderm give rise to extra embryonic structures that support growth

neg: Introduction to evolution forms. As the embryo develops, these homologies can be lost to view, and the structures can take on different functions. Part of the basis of classifying the vertebrate group (which includes humans), is the presence of a tail (extending beyond the anus) and pharyngeal slits. Both structures appear during some stage of embryonic development but are not always obvious in the adult form. Because of the morphological similarities present in embryos of different species during development, it was once assumed that organisms re-enact their evolutionary history as an embryo. It was thought that human embryos passed through an amphibian then

neg: Abortion in Afghanistan different stages they pass through, and the stage affects the acceptability of the procedure. Prenatal Development outlines these different stages. From conception, when the sperm and egg fuse in the fallopian tube, until week 5 of the pregnancy, it is referred to as the zygote. From week 5 until week 10 of the pregnancy, it is referred to as an embryo. At week 10 in the pregnancy, the embryo becomes a fetus and development of all organ systems and body parts begins. At around the 38-40th week, a fully developed baby will be born. For Islam followers, once the cells

neg: Embryo donation the recipients. No one knows for sure when the first true embryo adoption occurred. The term was used as early as the mid-1980s, in the legal literature. Devroey et al., Dr. Maria Bustillo in Florida, and Dr. Howard Jones in Virginia have reported embryo transfers occurring between 1986 and 1990 that clearly represented adoption of remaining embryos. Prior to this, thousands of women who were infertile had regarded adoption as the only available path to parenthood. These scientific advances set the stage to allow open and candid discussion of embryo donation and transfer as a solution to infertility. In some

neg: Austrolestes colensonis well developed embryos that can push through the winter in a state of quiescence. Temperature was the major influence that regulated the rate of development; any temperature near or below the threshold inhibited early embryonic development and eventually caused death to the embryo. Eggs can be hatched in about 20–21 days at 20 degrees Celsius, in others the developed embryo forms the overwintering stage. Before emergence, the nymphal darkens until it is near black. Rowe (1987) found that the nymphs may take several short trips from the water a few days before emergence, which takes place on rush stalks 10–40