Analysis of genetic diversity in a close population of Zandi sheep using genealogical information

Abstract

In a Fisher–Wright idealized population (Fisher 1930; Wright 1931), characterized by Poisson distribution of family size, large number of breeders, random mating, equal sex ratio, absence of selection, mutation, or migration, and discrete generations, the rate of loss of heterozygosity is inversely proportional to population size. In real populations, however, genetic diversity is affected by several ongoing natural processes of mutation, migration, genetic drift and selection. For this reason, Wright (1931) proposed the concept of the effective population size (Ne) for extending population genetics theory developed for ideal populations to real populations. This parameter has been useful in designing strategies for conservation of endangered animal species because of its direct relationship with the level of inbreeding (Caballero and Toro 2000). However, when Ne is estimated from pedigree data, the parameter accuracy may be affected by several factors, as extensively reviewed by Boichard et al. (1997). Consequently, in recent decades, new complementary techniques have been developed for the analysis of genealogies. Lacy (1989) introduced the concept of effective number of founders ( fe) in order to measure the overall founder representation in a managed population accounting for the loss of genetic diversity from unequal founder contributions, and the concept of founder genome equivalents ( fg), also called effective number of founder genomes, to account the effects of bottlenecks, unequal founder contributions, and genetic drift. Boichard et al. (1997) developed the concept of effective number of ancestors ( fa) to supplement the effective number of founders. The numbers obtained from