UV action on the genetic combination after irradiation of polar cap cells of Drosophila females; heterozygous for markers localized on chromosome III

Abstract

In order to irradiate oogenic primordial germ cells with 2537 Å UV light of slight penetrating ability, polar cap cells were exposed. Heterozygous markers on the third chromosome enabled us to measure the crossing-over among progeny from treated cells. Two distinct effects of UV can be observed; one is on mitotic recombination and the other on meiotic recombination. 1. (1) Induction of mitotic recombinations. (a) Progenies from three single females having clusters of cross-overs were found. These clusters were related to UV-induced mitotic recombinations during the first division following irradiation time. (b) Mitotic recombinations were induced in the centromeric region. 2. (2) Increasing of meiotic recombination frequencies. (a) Although some variability exists, crossing-over among descendants from the UV-treated flies was consistetnly higher than spontaneous crossing-over. (b) These UV-induced meiotic cross-over were predominantly found in the centromeric region. (c) This effect is photoreactivable. (d) Although premeiotic cells were exposed to the UV light, meiotic cells were affected which may indicate a delay in the time of action. The most likely hypothesis is that UV produces some physiological damage. This disturbing of metabolic activity might be the primary influence on meiotic crossing-over.