Variability of polyteny of giant chromosomes in Drosophila melanogaster salivary glands.

Polyteny is an effective mechanism for accelerating growth and enhancing gene expression in eukaryotes. The purpose of investigation was to study the genetic variability of polyteny degree of giant chromosomes in the salivary glands of Drosophila melanogaster Meig. in relation to the differential fitness of different genotypes. 16 strains, lines and hybrids of fruit flies were studied. This study demonstrates the significant influence of hereditary factors on the level of polytenization of giant chromosomes in Drosophila. This is manifested in the differences between strains and lines, the effect of inbreeding, chromosome isogenization, hybridization, adaptively significant selection, sexual differences, and varying degrees of individual variability of a trait in different strains, lines, and hybrids. The genetic component in the variability of the degree of chromosome polyteny in Drosophila salivary glands was 45.3%, the effect of sex was 9.5%. It has been shown that genetic distances during inbreeding, outbreeding or hybridization, which largely determine the selective value of different genotypes, also affect polyteny patterns. Genetic, humoral, and epigenetic aspects of endocycle regulation, which may underlie the variations in the degree of chromosome polyteny, as well as the biological significance of the phenomenon of endopolyploidy, are discussed.

Endoreduplication in Drosophila melanogaster progeny after exposure to acute γ-irradiation.

The purpose of this investigation was to study the effect of acute γ-irradiation of parent adults on the endoreduplication of giant chromosomes in F1 generation of Drosophila melanogaster Meig. A wild-type Oregon-R strain was used as the material. Virgin females and males of Drosophila adults at the age of 3 days were irradiated with doses of 8, 16 and 25 Gy. Giant chromosomes were studied by cytomorphometry on squashed preparations of Drosophila salivary glands stained with acetoorsein. The preparations were obtained at late third instar larvae. The mean values of the polyteny degree of chromosomes (PDC) in males increased after 8 Gy by 10.6%, after 25 Gy by 7.4%, and did not change after the dose of 16 Gy. In females, the PDC did not differ from the control irrespective of the irradiation dose. An increase in endoreduplication was also evidenced by the accelerated development of offsprings of both sexes after irradiation of parents with 25 Gy, and in males also at a dose of 16 Gy. The statistical impact of power of radiation on polyteny was 26.8%, while the impact of sex was 4.9%. The impact of power of radiation on the developmental rate of offspring was 4.4% in males and 7.5% in females. The enhancement of endoreduplication is considered as a consequence of increasing selection pressure after irradiation. The possible involvement of epigenetic effects in the effect of ionizing radiation on endoreduplication is discussed.