Long-term effects of selection based on the animal model BLUP in a finite population

Abstract

Monte Carlo simulation was used to assess the long-term effects of truncation selection within small populations using indices (I=ωf+m) combining mid-parent [f=(a i+a d)/2] and Mendelian-sampling (m=a-f) evaluations provided by an animal model BLUP (a=f+m). Phenotypic values of panmictic populations were generated for 30 discrete generations. Assuming a purely additive polygenic model, heritability (h 2) values were 0.10, 0.25 or 0.50. Two population sizes were considered: five males and 25 females selected out of 50 candidates of each sex (small populations, S) and 50 males and 250 females selected out of 500 candidates in each sex (large populations, L). Selection was carried out on the index defined above with ω = 1 (animal model BLUP), ω=1/2, or ω=0 (selection on within-family deviations). Mass selection was also considered. Selection based on the animal model BLUP (ω=1) maximized the cumulative genetic gain in L populations. In S populations, selection using ω = 1/2 and mass selection were more efficient than selection under an animal model (+ 3 to + 7% and + 1 to + 4% respectively, depending on h (2)). Selection on within-family deviations always led to the lowest gains. In most cases, the variance of response to selection between replicates did not depend on the selection method. The within-replicate genetic variance and the average coefficient of inbreeding (F) were highly affected by selection with ω=1 or 1/2, especially in populations of size S. As expected, selection based on within-family deviations was less detrimental in that respect. The number of copies of founder neutral genes at a separate locus, and the probability vector of origin of the genes in reference to the founder animals, were also observed in addition to F values. The conclusion was that selection procedures placing less emphasis on family information might be interesting alternatives to selection based on animal model BLUP, especially for small populations with long-term selection objectives.

Strategies for controlling rates of inbreeding in MOET nucleus schemes for beef cattle

“…They showed that, in this way, inbreeding rates can be reduced with only a small loss in response. This also agrees with the results obtained by Toro and Silio (1993 (Dempfle, 1975;Verrier et al, 1993 (Nicholas, 1989). Theoretical work is needed to compare objectively the different procedures suggested to control rates of inbreeding and to find optimum schemes setting the genetic gains from selection against the losses due to inbreeding.…”

Oscilação genética em populações submetidas a métodos de seleção tradicionais e associados a marcadores moleculares

“…Verrier et al (1993) utilizaram simulação para verificar os efeitos da seleção a longo prazo em pequenas populações submetidas à seleção pelos valores genéticos preditos pelo BLUP sob modelo animal e observaram que, nas populações de pequeno tamanho, o efeito da oscilação foi maior, enquanto a variância genética decresceu rapidamente. Em contraste, em populações de tamanho maior, o efeito da oscilação não foi tão grande e a variância genética se manteve.…”

Comparação de métodos de seleção em populações simuladas de frangos de corte

“…Valor fenotípico mais eficiente a escolha dos melhores indivíduos para a reprodução, visto que são utilizadas todas as informações disponíveis dos parentes de candidatos à seleção, de forma a otimizar a resposta genética em curto prazo (Verrier et al, 1993). Robinson et al (1989) compararam o progresso genético, durante 20 gerações, resultante da avaliação dos animais com utilização do BLUP e de um índice de seleção.…”

“…Verificaram que, em geral, o BLUP proporcionou maior resposta genética do que o índice de seleção proposto. Verrier et al (1993), ao verificarem os efeitos da seleção, em pequenas e grandes populações, usando um índice de seleção BLUP e seleção individual, concluí-ram que a seleção com o BLUP maximizava o ganho genético em grandes populações.…”