What are the reasons behind occurrence of inbreeding depression?
Inbreeding depression is the reduction in the fertility and productivity of an organism due to continuous inbreeding. Inbreeding refers to the mating of closely- related individuals within the same breed. Continued inbreeding especially close inbreeding usually reduces the fertility and even productivity of an organism.
When two related individuals (having common ancestry) breed, it leads to a population with leads reduced fitness and physiological vigour. This is inbreeding depression. It occurs due to the accumulation of a single genotype, resulting in the expression of recessive traits and increased genetic load.
For example, autogamy and geitonogamy in plants often leads to inbreeding depression.