A TEST FOR RECOMBINATIONAL LETHALS IN THE X-CHROMOSOME OF DROSOPHILA MELANOGASTER

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Abstract
One male from each of 10 wild-type stocks of divergent origin was mated with y f attached-X females. The F1 wild-type males, which had received the X chromosome from the male parent, were mated with attached-X sibs to perpetuate the wild-type X chromosome without recombination. In the experimental crosses a female, carrying both the wild-type X chromosome from 1 stock and a crossover-suppressor X chromosome (inversion), was crossed with 3 or 4 males with wild-type X chromosomes from a 2d stock. In the F1, 4 females with the 2 wild-type X chromosomes (identifiable by not showing the gene markers of the inverted chromosomes) were mated with 4 males carrying a 2d type of crossover-suppressor X chromosome. In the 3d generation 25 females with the markers of the crossover-suppressor X chromosome were mated separately with 4 males of the genotype used in the second generation matings. Fifteen days later offspring were checked for lethals carried by the females in the 3d generation. These females may have carried an unchanged wild-type X chromosome from either of the original stocks or parts of both chromosomes if recombination had occurred in the F1 females. Various criteria were used in detecting the presence or absence of lethals. Of 10 control combinations (homozygous for each of the different sources of wild-type X chromosomes), 0.10% lethals were found in 994 chromosomes tested. Of the 45 combinations heterozygous for the X chromosomes, 0.25% lethals were found in 5186 chromosomes tested. The difference between these 2 frequencies was not statistically significant. Genetical tests of the lethals indicated that they all had specific loci and were not due to recombination.