The purpose of investigation was to study the effect of acute γ-irradiation of parent adults on the endoreduplication in Drosophila melanogaster progeny. As a material used Oregon-R strain. Virgin females and males of Drosophila adults at the age of 3 days were exposed at the doses of 8, 16 and 25 Gy. Giant chromosomes were studied at late 3rd instar larvae by cytomorphometric method. The average polyteny in males increased at the dose of 8 Gy by 10.6%, at the dose of 25 Gy by 7.4%, and did not change at the dose of 16 Gy. In females, the polyteny did not differ from the control value irrespective of the irradiation dose. The statistical impact power of sex on polyteny was 4,9%, the radiation impact was 26,8%. The enhancement of endoruplication is considered as a consequence of an increasing selection pressure after irradiation.

Aim. The purpose of investigation was to study the intensity of selection in two generations of Drosophila melanogaster Meig. after acute g-irradiation. Methods. Experiments were conducted on a wild-type Oregon-R strain. Adult flies in the age of 3 days were irradiated with bremsstrahlung gamma quanta at doses of 8 Gy, 16 Gy and 25 Gy on a linear accelerator of electrons LAE-10. Irradiated (O) and non-irradiated (K) flies were crossed in four different combinations: K×K (control), O×K, K×O, and O×O. The selection index were calculated from the Crow formula based on fertility, mortality/survival in pre-productive period of development. Results. Selection indexes in the generation F1 after irradiation grow in proportion to the dose received: at embryonal stage 2.0–7.2 times, at post-embryonic development – in 1.3–7.6 times. In the generation F2, the indexes of selection were significantly reduced. Conclusions. The selection pressure is substantially increased in the first generation after g-irradiation and weakens, approaching the control level and lower in F2. Keywords: Drosophila melanogaster Meig., fertility, embryonic mortality, pupae mortality, ionizing radiation.

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 effect size of the genotype on the degree of chromosome polyteny in Drosophila salivary glands was 45.3%, the effect size of sex was 9.5%. The data obtained allow us to conclude that the variations in the level of polyteny should be considered as a manifestation of the structural and functional polymorphism of giant chromosomes, which is an essential factor in the differential fitness of flies and has a selective value.

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 tness of different genotypes. 16 strains, lines and hybrids of fruit ies were studied. This study demonstrates the signi cant in uence 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 signi cant selection, sexual differences, and varying degrees of individual variability of a trait in different strains, lines, and hybrids. The effect size of the genotype on the degree of chromosome polyteny in Drosophila salivary glands was 45.3%, the effect size of sex was 9.5%. The data obtained allow us to conclude that the variations in the level of polyteny should be considered as a manifestation of the structural and functional polymorphism of giant chromosomes, which is an essential factor in the differential tness of ies and has a selective value.