What does meiosis have to do with genetic diversity ?

Genetic variation is increased by meiosis. During fertilisation, 1 gamete from each parent combines to form a zygote. Because of recombination and independent assortment inmeiosis, each gamete contains a different set of DNA. This produces a unique combination of genes in the resulting zygote.

Crossing Over. During prophase of meiosis I, the double-chromatid homologous pairs of chromosomes cross over with each other and often exchange chromosome segments. This recombination creates genetic diversity by allowing genes from each parent to intermix, resulting in chromosomes with a different genetic complement.

Genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis(which reshuffles alleles within an organism's offspring).

Meiosis is sex cell division, sex cells mainly being genes. When the father or the mother have dominant allele the child gets the same allele but with a recessive allele too.
For the second generation, this difference in phenotype and genotype will cause a clear genetic diversity. The same continues for the rest generation too.

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