The most important biological role of meiosis compared with asexual reproduction is providing genetic diversity of individuals as a result of “mixing”¯ of paternal and maternal genes in the gamete. This is achieved in two ways.
Firstly, in the first division of meiosis the distribution of paternal and maternal chromosomes into the daughter cells is random, which results in gametes bearing different combinations of parental chromosomes (Smith and Nicolas 204). The second fundamental mechanism for the maintenance of genetic diversity is that in the initial phase of the first meiotic division homologous chromosomes are arranged opposite to each other and couple, forming one or more areas of contact (chiasm) between individual unsisterly chromatids. Next, the pair of chromatids that formed chiasm exchanges the sections of DNA (crossing-over process). As a result of crossing-over recombinant chromosomes are formed consisting of sections originating from different parent lines. Upon the completion of meiosis the recombinant chromosomes disperse to different gametes. Thus, crossing-over represents a special case of genetic recombination – the process of redistribution of genetic material of parents during its transmission to posterity. An important consequence of crossing-over is the creation of a new combination of genes in the offspring during the connection of parental gametes (Smith and Nicolas 205-7).
Thus, meiosis is the mechanism that provides a diversity of gametes produced by the same body, in the course of which not only the hereditary material falling into the gametes is reduced by half, but also parental alleles are effectively redistributed among gametes. The processes leading to recombination of genes and whole chromosomes in germ cells are crossing-over and divergence of bivalents in meiosis anaphase I. At the same time, the same processes provide individual hereditary differences of individuals which are based on the recombination of genes and chromosomes, i.e. combinational variability (Smith and Nicolas 208). Combinational variability manifested in the genotypic diversity of individuals increases the survival of the species in the changing conditions of its existence.