Genetics of Natural Populations. Xxxii. Inbreeding and the Mutational and Balanced Genetic Loads in Natural Populations of Drosophila Pseudoobscura

GENETIC LOADS AFFECTING FECUNDITY IN NATURAL POPULATIONS OF DROSOPHILA PSEUDOOBSCURA

“…Because of the small samples in the separate localities, the figures vary from 17% (Chiricahua) to 43% (Bryce). The range recorded for D. pseudoobscura by DOBZHANSKY, SPASSKY and TIDWELL (1963) is 18 to 32%, but it is not necessary to assume that any of our populations had abnormally heavy or light viability loads. The mean percentage of non-Bare flies in the cultures of all 256 second-chromosome homozygotes turns out to be 22.64 + 0.79%, and eliminating the lethals and semilethals, 28.93 * 0.42%.…”

Lethal and Semilethal Chromosomes in Irradiated Experimental Populations of Drosophila Pseudoobscura

“…Yet, the figures for the freshly irradiated chromosomes (the rightmost column in Table 4) show that subvital changes were induced by the irradiation. The mean viability of quasi-normal homozygotes from natural populations is also distinctly below that of the heterozygotes (see Table 5 in DOBZHANSKY, SPASSKY and TIDWELL 1963;SPASSKY et al 1960;DOBZHANSKY et al 1963, and other publications). Most of the subvital mutations induced by the irradiation in our experimental populations have evidently been eliminated by natural selection.…”

Inbreeding and the Mutational and Balanced Loads in Natural Populations of Drosophila Willistoni

“…On the other hand, the total load estimated from the chromosome analysis is approximately three times that estimated from the inbreeding experiment; again strongly suggesting more than proportional effects on viability when the number of homozygous loci becomes large. DOBZHANSKY et al (1963) calculated the viability ratios by a slightly different method than the one used here. We have recalculated them by the same method used in the present paper, and used them to obtain new T values, both for the sake of comparability and to provide standard errors.…”

“…Similar experiments, giving closely similar estimates of the A and B values, were reported by STONE, WILSON and GERSTENBERG (1963). DOBZHANSKY, SPASSKY and TIDWELL (1963) also approached the problem of the magnitude of the inbreeding effects by another method, previously used for studies on genetic loads in several species of Drosophila. This method consists in obtaining individuals homozygous for certain chromosomes, by means of a series of crosses using genetic markers and suppressors of recombination in the chromosomes under investigation.…”

“…Complete counts of the adult flies hatching in the cultures were made. The techniques used were thus very similar, except for the half-sib matings, to those employed by DOBZHANSKY, SPASSKY, and TIDWELL 1963).…”