Inbreeding and Inbreeding Depression
Definition of Inbreeding:
Inbreeding is a form of mating system in sexual organism. It implies mating together of individual that are close to each other by ancestral or pedigree relationship.
When the individuals are closely related E. g Full sib was mating, half sib mating. The highest degree of inbreeding is achieved by selfing. The chief effect of inbreeding is to increase homozygosity in the progeny, which is proportionate to the degree of inbreeding. Cross – pollinated and asexually reproducing species are highly heterozygous in nature. These species show a severe reduction in fertility and vigour due to inbreeding (inbreeding depression). It contrast to this hybridization between unrelated strains leads to an increased vigour and fertility (hybrid vigour or heterosis). These two aspects are of great significance in breeding of these species. In fact heterosis and inbreeding depression may be considered as the two opposite sides of the same coin.
It refers to decrease in fitness and vigour due to inbreeding or it may be defined as the reduction or loss in vigour and fertility as a result of inbreeding.
The most revealing impact of inbreeding is the loss of vigour and the physiological efficiency of an organism characterised by reduction in size and fecundity. For example selfing reduces heterozygosity, by a factor ½ in each generation. In fact the dwgree of inbreeding in any generation is equal to the degree of homozygosity in that generation. Inbreeding depression results due to fixation of unfavourable recessive genes in F2, while in heterosis the unfavourable recessive genes of one line (parent) are covered by favourable dominant genes of other parent.
Man has recognised inbreeding depression for a long time. In many species marriage between closely related ancestries have been prohibited. In hindu society perhaps presents the extreme example, where marriages between individual related by ancestry is prohibited.