A zygote ( / ˈ z aɪ ˌ ɡ oʊ t / ; from Ancient Greek ζυγωτός (zygōtós) 'joined, yoked', from ζυγοῦν (zygoun) 'to join, to yoke') is a eukaryotic cell formed by a fertilization event between two gametes . The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. The sexual fusion of haploid cells is called karyogamy , the result of which is the formation of a diploid cell called the zygote or zygospore.
15-408: German zoologists Oscar and Richard Hertwig made some of the first discoveries on animal zygote formation in the late 19th century. The zygote is the earliest developmental stage. In humans and most other anisogamous organisms, a zygote is formed when an egg cell and sperm cell come together to create a new unique organism. The formation of a totipotent zygote with the potential to produce
30-528: A Refutation of Darwin's Theory of Chance"). Hertwig was elected a member of the Royal Swedish Academy of Sciences in 1903. Hertwig is known as Oscar Hedwig in the book "Who discovered what when" by David Ellyard. A history of the discovery of fertilization for mammals including scientists like Hertwig and other workers is given by the book "The Mammalian Egg" by Austin. Friedberg, Hesse Too Many Requests If you report this error to
45-478: A professor of zoology in Munich from 1885 to 1925, at Ludwig Maximilian University , where he served the last 40 years of his 50-year career as a professor at 4 universities. Hertwig was a leader in the field of comparative and causal animal-developmental history. He also wrote a leading textbook. By studying sea urchins he proved that fertilization occurs due to the fusion of a sperm and egg cell. He recognized
60-423: A released ovum (a haploid secondary oocyte with replicate chromosome copies) and a haploid sperm cell ( male gamete) combine to form a single diploid cell called the zygote. Once the single sperm fuses with the oocyte, the latter completes the division of the second meiosis forming a haploid daughter with only 23 chromosomes, almost all of the cytoplasm, and the male pronucleus . The other product of meiosis
75-476: A whole organism depends on epigenetic reprogramming. DNA demethylation of the paternal genome in the zygote appears to be an important part of epigenetic reprogramming. In the paternal genome of the mouse, demethylation of DNA, particularly at sites of methylated cytosines, is likely a key process in establishing totipotency. Demethylation involves the processes of base excision repair and possibly other DNA-repair–based mechanisms. In human fertilization ,
90-548: Is inherited uniparentally from the mt+ mating type parent. These rare biparental zygotes allowed mapping of chloroplast genes by recombination. Oscar Hertwig Oscar Hertwig (21 April 1849 in Friedberg – 25 October 1922 in Berlin ) was a German embryologist and zoologist known for his research in developmental biology and evolution . Hertwig is credited as the first man to observe sexual reproduction by looking at
105-452: Is the second polar body with only chromosomes but no ability to replicate or survive. In the fertilized daughter, DNA is then replicated in the two separate pronuclei derived from the sperm and ovum, making the zygote's chromosome number temporarily 4n diploid . After approximately 30 hours from the time of fertilization, a fusion of the pronuclei and immediate mitotic division produce two 2n diploid daughter cells called blastomeres . Between
120-724: Is the substance responsible not only for fertilization but also for the transmission of hereditary characteristics. This early suggestion was proven correct much later in 1944 by the Avery–MacLeod–McCarty experiment which showed that this is indeed the role of the nucleic acid DNA . While Hertwig was interested in developmental biology and evolution, he was opposed to chance as assumed in Charles Darwin ´s theory. His most important theoretical book was: "Das Werden der Organismen, eine Widerlegung der Darwinschen Zufallslehre" (Jena, 1916) (translation: "The Origin of Organisms –
135-539: The cells of sea urchins under the microscope. Hertwig was the elder brother of zoologist-professor Richard Hertwig (1850–1937). The Hertwig brothers were the most eminent scholars of Ernst Haeckel (and Carl Gegenbaur ) from the University of Jena . They were independent of Haeckel's philosophical speculations but took his ideas in a positive way to widen their concepts in zoology . Initially, between 1879 and 1883, they performed embryological studies, especially on
150-437: The conceptus travels down the fallopian tube towards the uterus while continuing to divide without actually increasing in size, in a process called cleavage . After four divisions, the conceptus consists of 16 blastomeres, and it is known as the morula . Through the processes of compaction, cell division, and blastulation, the conceptus takes the form of the blastocyst by the fifth day of development, just as it approaches
165-471: The role of the cell nucleus during inheritance and chromosome reduction during meiosis : in 1876, he published his findings that fertilization includes the penetration of a spermatozoon into an egg cell. Hermann Fol also observed this in the same year. Hertwig's experiments with frog eggs revealed the 'long axis rule', or Hertwig rule . According to this rule, cell divides along its long axis. In 1885 Hertwig wrote that nuclein (later called nucleic acid )
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#1732791240858180-408: The site of implantation. When the blastocyst hatches from the zona pellucida , it can implant in the endometrial lining of the uterus and begin the gastrulation stage of embryonic development. The human zygote has been genetically edited in experiments designed to cure inherited diseases. In fungi, this cell may then enter meiosis or mitosis depending on the life cycle of the species. In plants,
195-542: The stages of fertilization and implantation , the developing embryo is sometimes termed as a preimplantation- conceptus . This stage has also been referred to as the pre-embryo in legal discourses including relevance to the use of embryonic stem cells. In the US the National Institutes of Health has determined that the traditional classification of pre-implantation embryo is still correct. After fertilization,
210-443: The theory of the coelom (1881), the fluid-filled body cavity. These problems were based on the phylogenetic theorems of Haeckel, i.e. the biogenic theory (German = biogenetisches Grundgesetz), and the " gastraea theory ". Within 10 years, the two brothers moved apart to the north and south of Germany . Oscar Hertwig later became a professor of anatomy in 1888 in Berlin ; however, Richard Hertwig had moved 3 years prior, becoming
225-581: The zygote may be polyploid if fertilization occurs between meiotically unreduced gametes. In land plants , the zygote is formed within a chamber called the archegonium . In seedless plants, the archegonium is usually flask-shaped, with a long hollow neck through which the sperm cell enters. As the zygote divides and grows, it does so inside the archegonium. The zygote can divide asexually by mitosis to produce identical offspring. A Chlamydomonas zygote contains chloroplast DNA (cpDNA) from both parents; such cells are generally rare, since normally cpDNA
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