Genetic variability and population structure based on pedigree information for Muzaffarnagari sheep in India

Abstract

Abstract The objective of this study was to use pedigree analysis to evaluate the population structure and retention of genetic diversity in a flock of Muzaffarnagari sheep in India. Pedigrees of 5955 animals born between 1974 and 2003 was used to estimate the generation interval, pedigree completeness, and rate and level of inbreeding. Effective population size and parameters characterizing probabilities of gene origin were computed for lambs born between 2001 and 2003. The average numbers of equivalent complete generations were 3.41 and 5.00 for the whole and reference populations, respectively. The mean generation interval was 3.42 years. Average inbreeding coefficients for animals in the whole and reference populations were 1.79 and 1.23 %, respectively, and the rate of inbreeding was 0.68 % per generation. The average additive relationships for all animals and those in the reference population were 3.93 and 6.43 %, respectively. The realized effective population size, estimated from either the increase in coancestry between pairs of individuals or by regression of the average inbreeding coefficient on number of equivalent complete generations was approximately 76. Probabilities of gene origin were estimated by calculating effective numbers of founders (fe), ancestors (fa), founder genomes (fg), and non-founder genomes (fng) (33, 30, 15.4, and 28.9, respectively). The 10 most influential ancestors accounted for 50 % of the genetic variability, with a maximum individual contribution 6.53 %. The fe/fa ratio in the reference population was 1.10, indicating that occasional bottlenecks had occurred. Approximately 3.2 % of the initial heterozygosity had disappeared from the population. The results revealed that although there was some evidences of bottlenecks and genetic drift, considerable genetic variability remained in the population.