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Induced recombination in the proximal regions of chromosome 2 in females of Drosophila Melanogaster Tattersall, Philippa Jill


In order to study and compare spontaneous and radiation induced recombination frequencies of the euchromatic and heterochromatic regions of chromosome 2 Drosophila melanogaster females were exposed to 0, 2, 3, 4, or 5 krads of gamma radiation. Exchange was measured in the b-Bl, Bl-It, lt-rl, rl-pk, and pk-cn intervals. The lt-rl interval defines a wholly heterochromatic segment. Analysis of the recombination data demonstrates that spontaneous recombination occurs in the heterochromatic interval at a frequency of approximately 0.1% and the frequency of induced recombination is primarily increased in the heterochromatic interval. Moreover, the frequency of recombination in the heterochromatic interval is correlated with the dose of radiation. There are slight or no increases in the recombination frequencies of the euchromatic segments and the regions containing the heterochromatic-euchromatic boundaries show responses intermediate to the heterochromatic and euchromatic regions. Testing of the recombinant chromosomes indicates that 22% of them are associated with recessive lethals. The association is greater in eggs laid the first four days after radiation treatment than in thoselaid five-eleven days after the radiation treatment. It is postulated that induced recombination can occur via symmetrical as well as asymmetrical interchange. The interchromosomal effect of chromosome 3_, heterozygous for In(3LR)DcxF, on recombination in chromosome 1_ has been studied. The results show that its effect is not significant in the heterochromatic region. Thus, the alterations in the recombination frequencies owing to radiation treatment appear to be independent of those owing to the interchromosomal effect. Recombination was also measured in the presence of the heterochromatic deficiency - Df(2R)MS2¹º. The results indicate that the frequency of recombination is decreased in the chromosome arm containing the deficiency and in the heterochromatic interval of the left arm. The euchromatic regions of the opposite arm show a slight increase in recombination. A higher number of multiple crossover progeny are recovered than would be expected according to map distances in the presence of the heterochromatic deficiency, Df(2R)MS2¹º, the heterozygous inversion, In(3LR)DcxF, and for double crossovers involving the heterochromatic region, but only at high doses of radiation.

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