Inbreeding depression is the decline in health, survival, and reproductive success that results from mating between closely related individuals. Such mating increases the chance that offspring inherit harmful genetic traits because they are more likely to receive identical alleles (i.e., the same version of a gene) from each parent. When these matching genes are harmful, their effects are stronger because there is no healthy version of the gene to counterbalance them.
Inbreeding depression is especially problematic in small or isolated populations, such as endangered species or livestock breeding, because it reduces genetic diversity and makes populations more vulnerable to diseases and environmental changes.
Examples of inbreeding depression are seen in many endangered species. For example, the Florida panther suffered from heart defects, low sperm quality, and other health problems due to a small breeding population. In plants, the endangered Clarkia franciscana, a rare wildflower in California, shows reduced seed production and lower survival rates caused by inbreeding.
Inbreeding depression can be countered by genetic rescue, which involves the introduction of unrelated individuals from another population of the same species, when such a population exists.