Inbreeding Depression and Genetic Load in Japanese Quail Originated from the Incross

Abstract

The effect of inbreeding on the traits in the incross, crossed reciprocally between inbred lins of the 2nd and 4th full-sib generation in Japanese quail, were observed for 3 weeks' eggs layed by the parental quail when they were 11 weeks of age. Inbreeding depression for the traits were calculated by weighted regression, and the genetic load was estimated by the formula of MORTON et al..
1) The fitness index was reduced from 56.2% in random matings to 6.0% by the 4th generation of full-sib matings. Therefore, successive full-sib matings were difficult to reproduce after 5th generation.
2) For every 10% increment in inbreeding coefficient, the inbreeding depression for hen-day egg production, viability to 4 weeks and fitness index were 3.38, 6.34 and 9.56%, respectively. The pecentage of egg set, fertility and hatchability also showed a tendency of inbreeding depression.
3) Even though the regression of traits on inbreeding coefficient was calculated from the inbred lines succeeded to maintain until the 5th full-sib generation, it was almost same with that calculated from the all line in full-sib mating.
4) The numbers of lethal equivalents which obtained by summing up hen-day egg production, percentage of egg set, fertility, hatchability and viability to 4 weeks was 7.5, and the load ratio B/A was 9.7.
5) It is suggested that inbreeding depression in quail is caused by decrease of heterozygosity of polygenes in may loci rather than by increase of homozygosity of deleterious genes, since genetic load in quail may be more segregational than mutational load.