Mitosis is the process of creating two daughter cells from one parent cell. In Figure 5 the example cell (Figure 5-A) has one chromosome. However, the cell is diploid - it contains two copies of the chromosome, one from each parent. Mitosis starts with the duplication of each chromosome to produce two sister chromatids (5-B). The sister chromatids line up along the center of the of the cell and are slowly pulled apart by protein fibers attached to the chromatids on one end and to the edge of the cell on the other. The cell membrane then constricts (5-C) to form a separate membrane around each new diploid cell, called daughter cells .

Meiosis incorporates the process of mitosis, but with a significant difference. After daughter cells are formed (Figure 6-A), they split again without duplicating their DNA, producing four haploid cells that contain a single copy of each chromosome (6-B). When haploid cells - such as an eggs and sperm - combine with each other, the full complement of chromosomes is restored.

Recombination

Figure 6 also illustrates recombination, the exchange of genetic material between sister chromatids. Portions of sister chromatids from different parents (represented by pink and blue) physically cross over and exchange segments during meiosis (6-C). The order of the genes on the chromosome remains the same, but the specific versions of the genes (the alleles) become shuffled. As illustrated, the alleles that were carried on the blue chromosome may now be mixed with those on the pink, creating a gamete with a different set of alleles than either parental cell (6-D).

Recombination is one of the primary reasons that offspring from the same parents do not look alike, as new combinations of alleles are formed in every gamete. Recombination is a key mechanism for maintaining genetic variability in successive generations.