A computer simulation evaluation of the role of mutations in finite populations on the response to directional selection: The generations required to attain maximum genetic variance.

The role of mutations in finite populations on response to artificial selection was investigated by a computer simulation model designed to mimic the biological model of pupal weight of Tribolium. Given the model, the results showed that with selection about 25-55 generations were needed for genetic variances to reach a maximum value depending on population size, selection intensity, and gene number. When effective population size was larger than 40 or the intensity of selection was high (less than 50% selected), selection had a dramatic effect in reducing the time to approach the maximum point of genetic variance.

Mutational variance for pupa weight in Tribolium castaneum.

Directional selection for heavier pupa weight in Tribolium castaneum was practiced for 18 generations in two replicates of an inbred line, each separately maintained in small population cages for more than 90 generations. Mutational variance was estimated in two ways, based on Hill's (1982a) prediction equation for response to directional selection where an equilibrium state between effective population size and variation created by new mutation is assumed. Estimates of mutational variance based on response to selection in a selected population and from a sire-offspring regression analysis in an unselected control population were in strong agreement within each replicate population.

Selection for mating propensity in irradiated populations of the cotton boll weevil.

Twelve generations of family selection for 10-day post-irradiation male mating propensity resulted in significant divergence between the selected and unselected control populations. Much of this divergence was the result of a decline in the control population which was believed to have been a function of both inbreeding and environmental effects. Significant correlated responses as measured by differences in the two populations for linear time trends of performance on generations of selection were observed for 10-day post-irradiation survival, percent survivors mating at 10 days, and 7-day egg production of unirradiated females.

A selection response plateau for radiation resistance in the cotton boll weevil.

Twenty generations of family selection in the cotton boll weevil for 14-day postirradiation survival to 10,000 rads of gamma irradiation has increased survival to nearly 90% as compared with about 35% in the unselected control population. Mean survival time has increased to 21.2 days in the selected population, as compared with 12.

Gene number estimation when multiplicative genetic effects are assumed - growth in flour beetles and mice.

Estimation of the number of segregating genes affecting a quantitative trait in populations initiated from a cross of two homozygous lines is considered. Experimental data, for the trait in question, is assumed available on total response to recurrent selection initiated in the F2 or F3 generation, the initial additive genetic variance and the heterosis exhibited in the F1 generation. Appropriate procedures when multiplicative genetic effects are assumed are developed and reasons for assuming multiplicative rather than additive effects are indicated.

Stabilizing Selection for Pupa Weight in TRIBOLIUM CASTANEUM.

Ninety-five generations of stabilizing selection for pupa weight in Tribolium castaneum resulted in a significant decrease in phenotypic variance, moderate reductions in additive genetic variance, but only slight changes in heritability for the trait. Sterility was significantly lower and the average number of live progeny per fertile mating was significantly higher in populations where stabilizing selection was practiced as compared with random selected populations. The results indicate that more genetic variability is being maintained than would be expected unless a fraction of the genes have a heterozygote advantage on the fitness scale.

Experimental evidence on limitations of the heritability parameter.

Two-way selection was practiced at three selection intensities for 21 day pupa weight inTribolium castaneum. Each of the 19 single-generation replicates of the project consisted of three populations, one each being selected upward and downward at 10, 30 and 50% selection intensities. Realized heritability for divergence was significantly lower for the least intense (50%) level than for the 10% and 30% selection intensities.

Sex differences in gene expression for pupa weight in long term selected lines of Tribolium.

Full-sib matings in two populations of Tribolium which had been selected for increased pupa weight for more than 85 generations resulted in a significant inbreeding depression in male progeny but showed no effect in the female progeny. An analysis of variance of a population produced by backcrossing the selected populations to the inbred lines originally used to establish the select populations (Design-III) indicated some genes were still segregating which produce dominance effects in males but not in females. The data support the hypothesis that a class of genes exists, associated with the autosomes, that differ in their dominance effects of pupa weight in the two sexes.

Correlated response in male and female sterility to selection for pupa weight in Tribolium castaneum.

The correlated responses in male and female sterility to 50 generations of individual selection for pupa weight in Tribolium were analyzed. Two replicate lines (S-lines) were selected for heavier pupa weight and stabilizing selection for pupa weight was practiced in two replicate control lines (C-lines). There was close agreement between replicates in both sets of lines for direct and correlated responses.

Heterozygosity in inbred lines of Tribolinm castaneum.

Two-way selection for 21-day pupa weight was conducted in two highly inbred lines of Tribolium castaneum. The results, after 17 generations of selection, indicated that one of these lines (CSI-10) possessed a moderate amount of genetic variation for the trait selected (21-day pupa weight).When the selected populations were allowed to mate at random for 13 generations, the mean pupa weight regressed to values close to the means in the populations prior to selection.

Genotype - hatch interactions as a source of bias in estimating genetic components of variance for eight-week weight in poultry.

Data on 16,557 chicks from 198 sire groups were analyzed to determine the importance of genotype-hatch interactions as sources of bias in the estimation of genetic parameters for eight-week weight in poultry. Estimates of heritability for eight-week weight obtained from a paternal half-sib correlation were .27±.