In a small population, which genetic factor is most associated with a higher risk of extinction?

• A. Increased gene flow
• B. Absence of interspecific competition
• C. Disruptive selection
• D. Decreased genetic diversity

Answer: (D)

The main idea here is that genetic diversity acts as the pool of variation a population can draw on to survive changing conditions. In a small population, random genetic drift can quickly weed out alleles simply by chance, so there’s less genetic variation left. With fewer different alleles, the population has less potential to adapt to new diseases, climate changes, or shifts in habitat. Inbreeding becomes more common as individuals are more likely to mate with relatives, which increases homozygosity and can reveal harmful recessive alleles, reducing overall fitness. This combination—less variation and more inbreeding—lowers survival and reproductive success, making extinction more likely.

Other factors like gene flow bringing in new alleles can help a small population by increasing diversity; a lack of interspecific competition or disruptive selection doesn’t inherently cause the same direct loss of genetic variation that drives extinction risk in small populations.