Spontaneous male recombination and visible mutations were observed in second and third chromosomes derived from an isogenic line, ID, previously found to exhibit a high recessive lethal mutation rate. All three types of events tend to occur very early in spermatogenesis resulting in large clusters of identical recombinant or mutant progeny from a single male. Mutations and male recombination exchange points tend to be located more frequently in the right arm than in the left in both second and third chromosomes but for a trivial reason in the case of chromosome 2. No significant differences in male or female recombination were found between the progeny of reciprocal crosses. Male recombination in chromosome 2, like recessive lethal mutation, is independent of the presence of ID third chromosomes in the same genome. Both quantitative and qualitative differences in male recombination were found when ID chromosomes were compared with others extracted from natural populations.

Animals↗

PubMedDate not supplied

Variation of the recombination fraction in Drosophila melanogaster females.

The distribution of the recombination fraction between two distal, autosomal loci, plexus and orange, was investigated in reciprocal crosses between the marker stock and each of two wild-type strains, Harwich and Ottawa. The dysgenic cross between Harwich males and marker females exhibited high sterility, low fecundity, and a non-normal distribution of the recombination fraction. Neither the distribution of the reciprocal Harwich cross nor those of the two Ottawa crosses deviated from normal. In general, the results support the view that the recombination fraction is a variable.

Animals↗

PubMedDate not supplied

Dynamics of natural selection on a lethal fourth chromosome of Drosophila. Twelve-generation study of experimental populations of D. melanogaster.

The dynamics of natural selection on a lethal fourth chromosome of Drosophila melanogaster was studied in replicated half-pint bottle and cage populations over 12 generations. Population numbers fluctuated widely in all populations, but there was no association between fluctuation in numbers and change in lethal frequency. In the bottle populations the lethal heterozygote frequency decreased to a low of 0.04 to 0.05 and then increased to 0.18 to 0.30, suggesting that the selection coefficients were not constant. In the cage populations heterozygote frequency decreased to about 0.35 to 0.40. In the cage populations the data suggest that the lethal chromosome is overdominant for both viability and fertility selection.

Animals↗

PubMedDate not supplied

Dynamics of correlated genetic systems. VI. Variation in recombination rates in experimental populations of Drosophila melanogaster.

Recombination fractions among four chromosome 3 enzyme loci were measured over a 20 generation period in experimental populations of Drosophila melanogaster. The experimental populations were initiated with complete pairwise linkage disequilibria among the marker loci, thereby providing an initial structure favorable to selection for recombination modification. The recombination data show no evidence of directional changes in recombination rates among the marker loci, although variation in estimates, both between families within generations and between generations was large. These materials also yielded much lower estimates for recombination fractions for the centromeric region of the third chromosome than previously reported. Taken in total, the experimental results show no evidence for recombination modification, although the results do indicate ample genetic variance for recombination rates.

Animals↗

PubMedDate not supplied

Effect of selection, mutation, and linkage on the equilibrium structure of selfing systems.

One-, two- and three-locus models of selection and mutation in completely self-fertilizing populations are examined. Equilibrium frequencies can be determined for these systems. Numerical analyses indicate that random genetic drift attributable to selfing plays a major role in determining equilibrium frequencies, even when strong directional selection is operating. Linkage has no effect on marginal gene frequencies or single-locus heterozygosity at equilibrium. The only model of those examined which leads to linkage disequilibrium is disruptive selection. In that model, selection reinforced the effect of selfing in favoring the homozygous genotypes.

Alleles↗