Why is genetic drift of particular importance when thinking about endangered species?

Answer 1

Genetic drift is the change in allele frequencies in a population over time due to chance, or "sampling error". Genetic drift occurs most often in small populations and decreases a population's genetic diversity (or variability). Genetic variation in a population allows individuals to adapt differently to environmental stressors. If individuals in a population lack genetic variability, they will have similar responses to stressors. For example, if all of the individuals in a population have genes that protect them against tick-bourne diseases but lack genes that protect them against mosquito-bourne diseases, the entire population could be wiped out if a mosquito-bourne disease was introduced.

Endangered species have smaller population sizes, and due to genetic drift they may also have decreased fitness, increased susceptibility to disease and parasites, and an overall diminished ability to respond and adapt to environmental or biological stressors.