The effect of radiation-induced mutations on the fitness of Drosophila populations

The change in frequencies of D. melanogaster and D. simulans in competition experiments was used to measure the effect of radiation on the fitness of a population. A dose of 250 or 500 rads given to the males of highly inbred lines of D. simulans at the beginning of competition and every three weeks thereafter increased the relative frequency of the irradiated population. If the dose was increased to 1000 rads, the deleterious effects of radiation became too great a burden on the population, and the frequency of the irradiated population decreased. From these results it was concluded that below certain doses the introduction of radiation-induced mutations into a highly homozygous population would increase the fitness of the population.

The effect of oxygen on the frequency of somatic recombination in Drosophila melanogaster

The influence of oxygen on the frequency of somatic recombination in the yellow singed system on the X chromosome of Drosophila melanogaster was studied under a variety of experimental conditions. Flies raised from egg to adult in atmospheres containing 70-90% oxygen were found to have significantly more mosaic spots on their abdominal tergites than were observed in flies which developed in air. First instar larvae X-rayed in from 0 to 100% oxygen demonstrated the existence of an oxygen effect for somatic recombination in the cells which form the abdominal hypoderm. The mosaic spot counts, beginning with the lowest numbers which were found in flies X-rayed in nitrogen, increased rapidly with rising oxygen tensions until the percentage in air was reached, then leveled off at the higher concentrations. Post-treatment with nitrogen of larvae X-rayed in air or oxygen created a substantially higher number of mosaic spots than were found when larvae, after being similarly irradiated, were instead placed into air or oxygen.

Developmental analysis of the wing disc in the mutant engrailed of Drosophila melanogaster

The engrailed (en) mutation leads to the transformation of the posterior structures of the dorsal mesothoracic disc into those characteristic of the anterior region of the same disc. Similar posterior-anterior duplications have been detected in dorsal as well as ventral structures of all the thoracic segments. -Genetic combinations of en with other pattern mutants have shown their synergistic effect on the posterior wing pattern.-A clonal analysis of the en wing disc shows that en affects its development in a characteristic way. The genetic change, by induced mitotic recombination, of en(+) into en cells is followed by the corresponding transformation, except when it takes place some cell divisions prior to differentiation.-The en posterior wing disc cells show positive affinities with normal anterior wing disc cells in aggregates.-The mode of action of the en(+) locus controlling wing disc development is discussed.

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.