Final answer:
Inbreeding depression occurs when closely related individuals mate, bringing together harmful mutations that can lead to decreased fitness and increased disease in the offspring.
Step-by-step explanation:
Inbreeding depression is the result of breeding between closely related individuals, which can lead to an increase in abnormalities and disease within inbred populations. This outcome is primarily due to the coming together of rare, deleterious mutations that may be carried by close relatives.
When these individuals mate, there's a higher probability that their offspring will inherit these harmful mutations in a homozygous state, leading to harmful phenotypes that can reduce fitness, survival, and reproductive capability. Inbreeding depression is a concern not only in natural populations but also in agriculture and animal breeding, where maintaining genetic diversity is crucial for the health and viability of crops and livestock.