Gamete

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A gamete (

fertilization in organisms that reproduce sexually.[1] Gametes are an organism's reproductive cells, also referred to as sex cells.[2] The name gamete was introduced by the German cytologist Eduard Strasburger.[when?][citation needed
]

Gametes of both mating individuals can be the same size and shape, a condition known as

ovum, and a male produces the smaller type, called a sperm cell or spermatozoon. Sperm cells are small and motile due to the presence of a tail-shaped structure, the flagellum, that provides propulsion. In contrast, each egg cell or ovum is relatively large and non-motile.[2]

diploid organism.[2]

Evolution

Main article: Evolution of sexual reproduction

It is generally accepted that isogamy is the ancestral state from which anisogamy and oogamy evolved, although its evolution has left no fossil records.[5][6][7] There are almost invariably only two gamete types, all analyses showing that intermediate gamete sizes are eliminated due to selection.[8][9] Since intermediate sized gametes do not have the same advantages as small or large ones,[10] they do worse than small ones in mobility and numbers, and worse than large ones in supply.[11]

Differences between gametes and somatic cells

In contrast to a gamete, which has only one set of chromosomes, a diploid somatic cell has two sets of homologous chromosomes, one of which is a copy of the chromosome set from the sperm and one a copy of the chromosome set from the egg cell. Recombination of the genes during meiosis ensures that the chromosomes of gametes are not exact duplicates of either of the sets of chromosomes carried in the parental diploid chromosomes but a mixture of the two.[12]

A human spermatozoon fusing with a human ovum. The spermatozoon is approximately 100,000 times smaller in size than the human ovum.

Artificial gametes

Artificial gametes, also known as in vitro derived gametes (IVD), stem cell-derived gametes (SCDGs), and in vitro generated gametes (IVG), are gametes derived from

surrogate mother would still be required for the gestation period.[13] Women who have passed menopause may be able to produce eggs and bear genetically related children with artificial gametes.[13] Robert Sparrow wrote, in the Journal of Medical Ethics, that embryos derived from artificial gametes could be used to derive new gametes and this process could be repeated to create multiple human generations in the laboratory.[14] This technique could be used to create cell lines for medical applications and for studying the heredity of genetic disorders.[14] Additionally, this technique could be used for human enhancement by selectively breeding for a desired genome or by using recombinant DNA technology to create enhancements that have not arisen in nature.[14]

Plants

anther and is non-motile, but can be distributed by wind, water or animal vectors. When a pollen grain lands on a mature stigma of a flower it germinates to form a pollen tube
that grows down the style into the ovary of the flower and then into the ovule. The pollen then produces non-motile sperm nuclei by mitosis that are transported down the pollen tube to the ovule where they are released for fertilization of the egg cell.

See also

Notes and references

  1. ^ "gamete | Definition, Formation, Examples, & Facts". Encyclopedia Britannica. Retrieved 20 October 2020.
  2. ^ a b c "gamete / gametes | Learn Science at Scitable". www.nature.com. Retrieved 20 October 2020.
  3. ^ Cotner, Sehoya; Wassenberg, Deena, "8.4 Sex: It's About the Gametes", The Evolution and Biology of Sex, retrieved 20 October 2020
  4. ISBN 978-1-108-49985-9
    .
  5. ISBN 978-0-08-091987-4
    .
  6. ISBN 978-93-259-9022-7
    .
  7. ISBN 978-0-674-03116-6
    .
  8. ISBN 978-3-0348-6273-8
    .
  9. PMID 25323972
    .
  10. ISBN 978-0-19-164701-7
    .
  11. S2CID 3741933
    .
  12. ^ "Mitosis, Meiosis, and Inheritance | Learn Science at Scitable". www.nature.com. Retrieved 1 March 2021. Consequently, the cells of the offspring have genes potentially capable of expressing some of the characteristics of both the father and the mother, subject to whether they are dominant or recessive.
  13. ^
    PMID 15738444. Pregnancies brought about by means of artificial gametes would necessarily require IVF
    techniques
  14. ^
    S2CID 959092
    . Retrieved 8 March 2015.
  15. ISBN 978-1015505667
    .
  16. ^
    PMID 11543285
    .
  17. S2CID 85257438
    .
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