Inbreeding refers to the mating of more closely related individuals within the same breed for 4-6 generations. Inbreeding increases homozygosity and can be used to produce pure lines. However, the continued breeding of closely related animals usually reduces fertility and productivity. This is called inbreeding depression. The cross between the members of the same breed which have no common ancestors for 4 to 6 generation. A single out cross often helps to overcome inbreeding depression.