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14.4: Fertilization

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  • Haploid cells that must fuse together are called gametes. Gametes do not grow by mitosis, they must fuse to another haploid cell to produce a zygote, the first diploid cell in an organism. This process is called fertilization and it is composed of two distinct stages: plasmogamy and karyogamy. During plasmogamy, the cytoplasm of the two gametes combines together (plasm- referring to cytoplasm, -gamy meaning marriage). In most organisms, karyogamy is simultaneous with plasmogamy and the nuclei of each gamete fuse together into a single diploid nucleus. When you learn about fungi, you’ll see that plasmogamy and karyogamy can be separated by long periods, resulting in a strange condition called being dikaryotic (having two nuclei).

    Each gamete produced during meiosis is genetically distinct, resulting in a pool of genetic options. During sex, organisms don’t choose which gametes are combined, so any combination of genes from the two parents is possible. This is called random fertilization and exponentially increases the potential for diversity within a population.

    How many different zygotes could you make by combining the following two sets of gametes produced by meiosis?

    Parent 1 eggs Parent 2 sperm
    1 1
    2 2
    3 3
    4 4

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