engleski

EVALUATION OF ANCESTRAL INBREEDING COEFFICIENTS: BALLOU’ S FORMULA VERSUS GENE DROPPING

The estimation of the purging of detrimental effect through inbreeding and selection is an important issue in the conservation genetics opening new perspectives for the management of small populations. In 1997 Ballou proposed the ancestral inbreeding coefficient, which is calculated recursively via pedigree inbreeding coefficients as a tool for evaluating the purging of deleterious alleles in zoo populations. The formula of Ballou assumes independence of inbreeding and ancestral inbreeding coefficients at any stage of the recursion. This study investigates the consequences of this inaccuracy on the estimation of true ancestral inbreeding, i.e. the proportion of alleles within a genome that has undergone inbreeding in the past. As an alternative we propose the estimation of ancestral inbreeding by the method of gene dropping. The methods are compared by stochastic simulations for various models with respect to mode of inheritance (neutral, detrimental and lethal alleles) and different settings for population size and initial allele frequencies. In all scenarios the proportion of alleles within a genome that has undergone inbreeding in the past was overestimated by Ballou’ s formula. Overestimation was not influenced by genetic model or initial allele frequency. The overestimation was more pronounced in smaller populations. In contrast, the ancestral inbreeding coefficient calculated by gene dropping provided an unbiased estimate of ancestral inbreeding in most models and settings. A marginal overestimation was observed only in models with lethal alleles. The results obtained suggest re-evaluation of studies where ancestral inbreeding has been estimated by Ballou's formula.

inbreeding coefficients; ballou’ s formula

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