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    Home > Biochemistry News > Biotechnology News > Scientists have solved an evolutionary question: why the size of a human egg is 10 million times that of a sperm cell

    Scientists have solved an evolutionary question: why the size of a human egg is 10 million times that of a sperm cell

    • Last Update: 2021-11-04
    • Source: Internet
    • Author: User
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    In most living animals, egg cells are much larger than sperm cells
    .
    Taking humans as an example, the size of a single egg is 10 million times that of sperm
    .

    In a new study, Northwestern University researchers solved the mystery: competition and natural selection caused this strange size difference
    .

    Researchers used mathematical models to propose that in the very early stages of evolution, primitive species reproduced through external fertilization
    .
    In this model, larger germ cells or gametes have a competitive advantage because they can provide more nutrients to potential zygotes
    .
    However, smaller gametes require fewer resources to make, which reduces the pressure on parents
    .

    The lead author of the study, Daniel Abrams, Professor of Engineering Science and Applied Mathematics at the McCormick School of Engineering, said: "Organisms need to use the most supplies to produce the largest gametes, or they need to use the least resources to produce the smallest gametes
    .
    Based on sex With reasonable assumptions of reproduction and natural selection, we believe that this difference in body size is almost inevitable
    .
    "

    The research was published in the online edition of The Journal of Theoretical Biology
    .
    The researchers’ model starts with isogamy, which is one of the sexual reproduction methods.
    In this state, all gametes are roughly the same size, and there are no different sexes
    .
    Then, the team developed and applied a simple mathematical model to illustrate how isogamy is transformed into anisogamy
    .
    In this state of anisogamy, the gametes either become very small or quite large
    .

    In this model, anisogamy is produced by competition in an environment with limited resources
    .
    If gametes are more advantageous in size than their neighbors, then they are more likely to survive, which leads to an "arms race" in favor of larger gametes
    .
    However, if the organism itself does not need more and more resources, it cannot produce a large number of germ cells
    .
    However, they can save resources by producing a large number of tiny gametes
    .

    "In the early evolution of sexual reproduction, gametes were symmetrical
    .
    But that's where the symmetry was broken.
    We eventually discovered that some organisms specialize in large gametes and others specialize in small gametes
    .
    "

    According to the author, a mystery that has not yet been solved is why some species that practice homosexual reproduction still exist
    .
    For example, some species of algae and fungi reproduce asexually or symmetrically mate
    .

    "Since Charles Darwin, there have been many different theories about the origin of heterozygous reproduction
    .
    " "The problems in evolutionary biology are difficult to test because we can only study today's species
    .
    We cannot see them for billions of years.
    The way it was before
    .
    Using mathematical models can generate new insights and understandings
    .
    "

    references:

    “A dynamical model for the origin of anisogamy” by Joseph D.
    Johnson, Nathan L.
    White, Alain Kangabire and Daniel M.
    Abrams, 18 March 2021,  Journal of Theoretical Biology .

    DOI: 10.


    1016/j.


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