While in mitosis, genes are generally transferred faithfully from one cellular generation to the next; in meiosis and subsequent sexual reproduction, genes get mixed up. Sexual reproduction actually expands the variety created by meiosis, because it combines the different varieties of parental genotypes.
This is because the melanocytes are located in the stratum basale. Lighter-skinned people usually have low basal levels, and exposure to UV radiation causes an increase which makes skin darker.
