Inbreeding and inbreeding depression Inbreeding is the mating of two individuals which are more closely related to each other than to the average of the population. It is well known from animal husbandry and plant cultivation that inbreeding often leads to a reduction of vitality. Inbred organisms seem to be more susceptible to disease, give smaller yields, and generally appear to have reduced fitness. This common phenomenon, known as 'inbreeding depression', is a major problem in animal breeding where inbreeding is, necessarily, the result of every selection. The reduction of performance can be explained in terms of a loss of genetic variability in the inbred genome*. According to recent hypothesis, the within-locus variability and the gene interactions resulting from heterozygosity are responsible for the phenomenon of inbreeding depression.