A chromosomal analysis of x-ray induced genetic variance of wing length in Drosophila melanogaster

A chromosomal analysis of genetic variation in wing length of Drosophila melanogaster was done using an isogenic line and a single derived irradiated line which differed significantly in wing length. Partitioning of the variance indicates no difference between X-ray induced genetic variance and that from other sources. Furthermore, the amount of additive variance is strongly dependent on chromosome frequency, and sex differences are present in all components.

Effects of radiation on populations of Drosophila melanogaster with different genetic structures. 3. Interaction with population size

A number of populations of D. melanogaster, varying in size from approximately 50 individuals to more than 5000, were chronically irradiated with 4000 r X-rays per generation and studied over a period of 40 generations to determine whether and to what extent the accumulation and equilibrium frequency of lethal chromosomes differed from one to the other. The overall fitness of these populations was studied by comparing the productivity of small samples taken from them, which were allowed to lay eggs and have their offspring develop under optimum conditions. The results of these experiments were as follows

Effects of radiation on populations of Drosophila melanogaster with different genetic structures. II. Temporal changes in the sex ratio

The effect of 1500 r X.rays, delivered for several generations to populations of D. melanoga8ter, on the sex ratio of the flies emerging has been examined. The results have been compared with those from similar populations living in the same environment but not given any radiation treatment. The mean values of four irradiated populations, when compared with their unirradiated counterparts, showed an initial drop in sex ratio followed by a marked recovery particularly between generations 7 and 12. When composite populations were set up, combining males from one irradiated population with females from another at each generation, this recovery in sex ratio was not observed. It was concluded that this latter result ruled out chromosomal phenomena and indicated a biometrical explanation as the most likely one for the observed rise in sex ratio with accumulated ancestral radiation in integrated gene pools

Effects of radiation on populations of Drosophila melanogaster with different genetic structures. I. Changes in fitness and productivity

It has been shown in previous work that heterozygotes between irradiated and non-irradiated populations of D. melanogaster experience a marked reduction in competitive ability. The effects of allowing the nucleus of a heterozygote gene pool to develop are here investigated and it is found that the total number emerging from a cage containing irradiated, non-irradiated, and heterozygote flies is considerably increased and the number of heterozygotes themselves shows almost a 100% increase. It is concluded that the opportunity given to the heterozygotes to form an integrated gene pool allows them to overcome much oftheir competitive disability.