Final answer:
Inbreeding significantly reduces genetic variance by increasing the likelihood that offspring will be homozygous for alleles, which includes potentially harmful recessive ones causing inbreeding depression.
Step-by-step explanation:
Inbreeding, the mating of closely related individuals, can have significant negative effects on a population's health and genetic diversity. One of these effects is the reduction of genetic variance, which refers to the variety of alleles and genotypes within a population. In a breeding context, like in zoos and nature preserves, scientists aim to increase a population's genetic variance to maintain phenotypic diversity. However, inbreeding brings together deleterious recessive mutations, leading to inbreeding depression. As such, inbreeding significantly reduces genetic variance to near zero because it increases the probability of offspring being homozygous for alleles, especially harmful recessive ones.