When the offsprings are produced by self fertilization or breeding between closely related parents it is called inbreeding. Inbreeding results in increase in homozygosity. The most revealing impact of inbreeding is the loss of vigour and physiological efficiency of the organisms characterized by reduction in size. A number of lethal and defective characters appear in the population which has undergone inbreeding (selfing). This loss of fitness in the progenies or decline in character expression with decreased heterozygosity arising from self mating is known as inbreeding depression or inbreeding decline. Continued inbreeding reduces fertility and even productivity. But the inbreeding progeny with lethal and harmful recessive genes being homozygous express these traits which otherwise remain hidden in heterozygous individuals. Natural selection works upon these individuals and eliminate them. Gradually, such genes get eliminated from the population.