Abstract
Genetic drift is caused by random sampling of alleles that contribute to the next generation, and results in loss of genetic diversity in populations. There are two sampling processes. First, sampling between families, i.e. some families become parents of the next generation, whereas others don’t. Second, Mendelian sampling of alleles within individuals. Without selection, both processes contribute approximately equal to loss of diversity. With selection (e.g. livestock), between family sampling causes the majority of the loss of diversity. Thus maintenance of diversity requires restriction of between family selection. Drift per unit of time is quantified by the variance of gene frequency change that can be attributed to a single generation or cohort,σq2. Drift causes homozygosity by descent (inbreeding), and drift variance and rate ofinbreeding (∆F) are equivalent measures of the loss of diversity,σq2= q(1-q)∆F. In livestock, the challenge is to genetically improve populations while maintaining diversity, i.e. to maximize gain (∆G) while restricting ∆F. The long-term genetic contribution theory reveals a relationship between ∆G and ∆F; ∆G = Σra and ∆F = *Σr2,where r is the long-term genetic contribution of an individual, a is its Mendelian sampling term and the sum is taken over all individuals per unit of time.It follows that the theoretical maximum gain with restricted in breeding is achieved by a linear increase of r with a. This provides a general measure of genetic efficiency of selection programs. Selection tools that maximize gain while restricting inbreeding try to establish this linear relationship by determining the optimum contribution of selection candidates to the next generation, which implicitly restricts between family selection. With restricted ∆F, minimum co ancestry and factorial mating increase ∆G. In addition, molecular markers enable reduction of Mendelian sampling drift, but benefits are small for livestock. Thus it is technically feasible to maximize ∆G while restricting ∆F. The commercial situation, however, may prohibit this. In particular in dairy cattle, global competition, availability of genetic material, and information on genetic quality (Interbull) causes breeding companies to focus on short-term improvement
Original language | English |
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Pages (from-to) | 11-11 |
Journal | Journal of Dairy Science |
Volume | 84 |
Issue number | suppl. 1 |
Publication status | Published - 2001 |