Most higher plants and animals exist in a diploid state in which their somatic cells have two of each type of chromosome. Why cannot a union of gametes produced by mitosis maintain this state of diploidy in the resultant individual? How does meiosis eliminate this problem, allowing diploidy to be maintained in subsequent generations? Does meiosis randomly divide chromosomes or insure that each gamete receives one of each type of chromosome from its parent?
Because mitosis produces new cells with exactly the same chromosomal content as the parent cell, a union of gametes produced by mitosis would double the normal number of chromosomes in each cell. Meiosis is the process of cell division by which gametes with half the number of chromosomes are created so when sperm and egg unite in sexual reproduction the diploid number of chromosomes is reconstituted. Thus, the number of chromosomes remains constant within a species from generation to generation. Meiosis does not randomly separate chromosomes but insures that each homologous chromosome pair in a diploid cell is divided so that each gamete contains one of each type of chromosome. Thus, gametes, said to be haploid, are cells with only one of each type of chromosome. Gametes join to produce a diploid zygote which receives half of its genetic material from the male parent and half from the female parent.
