Genetic variation in a line of mice selected to its limit for high body weight

Long-term selection for a quantitative character in large replicate populations of Drosophila melanogaster : Part 4: Relaxed and reverse selection

Reverse and relaxed selection were carried out in sublines which were derived from six replicate lines of Drosophila during 86-89 generations of selection for increased abdominal bristle number, and the reverse selection sublines were reciprocally crossed with selection lines of their origin.The results of serial relaxed selection initiated at different generations of selection confirm that the accelerated responses observed in the selection lines were largely due to deleterious genes, particularly lethals, with large effects on the selected character. The decline in mean bristle number under relaxed selection was not much different between crowded and uncrowded relaxed sublines.Reverse selection initiated at generation 57 was very effective, though it failed to bring the mean back to the base population level, and the genetic differences between replicate sublines (two from each of the six lines) indicate that low bristle number genes were probably rare in the selection lines. The genes which were still segregating after 57 generations of selection, on the average, did not show any directional dominance. The contribution of the X-chromosome to selection response was proportional to its chromosome length.

Maternal effects on body weight in mice selected for large and small size

Fertilized eggs were transferred reciprocally between large and small mothers, to study maternal effects on body weight in mice selected for large and small size, respectively. Prenatal maternal effects were not important in our material, but postnatal maternal effects were detectable. The postnatal effects accrued mostly from the inadequacy of small mothers for large offspring; small offspring were largely unaffected by the type of mother. Genetic maternal effects were only of limited importance; maternal influences of environmental origin arose from variation in litter size.

On the power of experimental designs for the detection of linkage between marker loci and quantitative loci in crosses between inbred lines

The power of experiments aimed at detecting linkage between a quantitative locus and a marker locus, both segregating in the backross or F2 generation of a cross between two inbred lines, is examined. Given that the two lines are close to fixation for alternative alleles of both marker locus and quantitative locus, it is concluded that experiments involving a few thousand offspring should be able to detect close linkages involving quantitative loci (or groups of loci) having rather modest effects (i.e., that contribute, say, 1% of the total phenotypic variance in the F2).