Final answer:
Genetic homozygosity in nearly extinct species leads to reduced genetic diversity, resulting in inbreeding depression and an increase in the prevalence of harmful recessive alleles, thereby elevating the risk of extinction.
Step-by-step explanation:
Genetic homozygosity is dangerous to a nearly extinct species because it reduces genetic variance, which is critical for the survival and adaptability of a species. A lack of genetic diversity can lead to inbreeding depression, where deleterious recessive alleles come together, resulting in an increased risk of abnormalities and susceptibility to diseases. This is particularly risky for small populations, which may have reduced genetic diversity due to small initial population size, making them vulnerable to recessive lethal alleles or changing environmental conditions.
For example, if a species is reduced to a few individuals, the chances of mating between close relatives become high and the offsprings are more likely to be homozygous for harmful recessive traits, manifesting into diseases or maladaptations. This genetic phenomenon is known as inbreeding depression and it can increase the extinction risk of the species. Inbreeding depression can be observed when purebred individuals with a small population size mate with each other, leading to a decrease in the population's overall health and fertility, and an increase in the frequency of inherited disorders.