| Popis: |
WHEN artificial selection is suspended in a selection program the mean of the population may shift depending upon the relationship of the observed trait with fitness and the effectiveness of natural selection in changing components of fitness such as egg production, fertility, hatchability, and viability. Lerner (1950) has discussed possible reasons for the decline of the population mean of previously selected traits when selection is relaxed. When selection for chicken shank length was suspended, hatchability increased but when selection was resumed, hatchability declined (Lerner, 1958). Moultrie et al. (1956) studied relaxed selection for three generations in a strain of disease-resistant White Leghorns. They observed a rise in leucosis mortality in the first generation which was sustained in the two succeeding generations. Shoffner and Grant (1960) relaxed the selection of Leghorns developed for egg production and found little if any decrease in egg production, hen housed viability, hatchability and eight-week body . . . |
