significant. The level of differentiation is the result of a balance between gene flow amongst sub-populations (decreasing differentiation) and genetic drift within these sub-populations (increasing differentiation); however, some molecular ecologists note that it cannot be assumed that these factors are at equilibrium. FST can also be viewed as a way of comparing the amount of inbreeding within sub-populations to the amount of inbreeding for the total population and is sometimes referred to as an inbreeding coefficient. In these cases, higher FST values typically imply higher amounts of inbreeding within the sub-populations. Other factors such as selection pressures may also affect FST values. FST values are accompanied by several analog equations (FIS, GST, etc.). These additional measures are interpreted in a similar manner to FST values; however, they are adjusted to accompany other factors that FST may not, such as accounting for multiple loci. Inbreeding depression Inbreeding depression is the reduced fitness and survival of offspring from closely related parents. Inbreeding is commonly seen in small populations because of the greater chance of mating with a relative due to limited mate choice. Inbreeding, especially in small populations, is more likely to result in higher rates of genetic drift, which leads to higher rates of homozygosity at all loci in the population and decreased heterozygosity. The rate of inbreeding is based on decreased heterozygosity. In other words, the rate at which heterozygosity is lost from a population due to genetic drift is equal to the rate of accumulating inbreeding in a population. In the absence of migration, inbreeding will accumulate at a rate that is inversely proportional to the size of the population. There are two ways in which inbreeding depression can occur. The first of these is through dominance, where beneficial alleles are usually dominant and harmful alleles are usually recessive. The increased homozygosity resulting from inbreeding means that harmful alleles are more likely to be expressed as homozygotes, and the deleterious effects cannot be masked by the beneficial dominant allele. The second method through which inbreeding depression occurs is through overdominance, or heterozygote advantage. Individuals that are heterozygous at a particular locus have a higher fitness than homozygotes at that locus. Inbreeding leads to decreased heterozygosity, and therefore decreased fitness. Deleterious alleles can be scrubbed by natural selection from inbred populations through genetic purging. As homozygosity increases, less fit individuals will be selected against and thus those harmful alleles will