Introduction to Genetic Drift

Mosquitoes, like humans, always carry two copies of each gene (except those on the sex chromosomes and in the mitochondrial genome). A mosquito can therefore either be heterozygous, carring different alleles on each homologous chromosome, or homozygous carrying the same allele on each chromosome. The germ cells are different from all other cells in the mosquito as they are the only ones to have a single copy of each homologous chromosome (haploid). These germ cells are formed from cells with two chromosome by meiosis, during which one of each pair of chromosomes is put into a different daughter cell. The process that determines which chromosome ends up in which germ cell is completely random, therefore during sexual reproduction it is random which allele gets passed from parent to child.