The effect of genetic drift in populations under selection with different effective sizes was evaluated using data simulated by the GENESYS program. Selection was applied during 20 generations based on Individual selection (IS) using breeding values predicted by classical best linear unbiased prediction (BLUP) and BLUP associated with molecular markers (BLUPM). The similarity matrix used in BLUPM was obtained by simulation of 100 micro-satellites markers (simple sequence repeats) using a similarity coefficient corresponding to the mean Euclidean distance for quantitative data. Six populations of selection were simulated corresponding to two effective sizes (18.18 and 66.66), and three mating systems of selected sires (random mating, exclusion of half sibs and exclusion of half as well as full sibs). The average phenotypic value was the parameter of evaluation. Large variation on average phenotypic values was due to genetic drift, mainly for BLUP and BLUPM methods and also for populations with small effective sizes. The results indicate genetic drift may cause large variation in genetic gains by selection in breeding programs designed for small populations.
BLUP; individual selection; genetic evaluation
