In Drosophila melanogaster two alleles, F and S, in the allozyme system Est‐6 were used to investigate sexual selection among different allelic genotypes. It was shown that sexual selection acts in the form of balancing selection between male and female genotypes. For certain genotypes, low sexual activity in one sex IS compensated for by a high activity in the opposite sex. This type of balancing selection was observed both at 16°C and 25°C, but the genotypes involved were homozygous SS at 16°C and homozygous FF at 25°C.

The components of phenotypic variation for mating activity, fertility and egg-adult viability were estimated in the leucine aminopeptidase-A and esterased allozyme systems in Drosophila melanogasfer. It was shown that variation among separate genotypes of these enzyme systems contributed considerably to the total phenotypic variation. For mating activity and fertility, 24% and 12% respectively of the total phenotypic variation was attributed to differences among allozyme genotypes, whereas for viability this component only amounted to 4%.

In Drosophila melanogaster two alleles, F and S, in the allozyme system Est‐6 were used to investigate sexual selection among different allelic genotypes. It was shown that sexual selection acts in the form of balancing selection between male and female genotypes. For certain genotypes, low sexual activity in one sex IS compensated for by a high activity in the opposite sex. This type of balancing selection was observed both at 16°C and 25°C, but the genotypes involved were homozygous SS at 16°C and homozygous FF at 25°C.

1978. The effects of number of Y chromosomes on mating behaviour and bristle number in Drosophila melanogaster. -Hereditas 89:24%254.Lund. Sweden.The effects of the dosage of Y chromosomes on some metrical characters in Drosophila melanogaster have been investigated. XO and XYY males were found to be considerably inferior than XY males in regard to mating activity, mating capacity and mating competition ability, while X X Y females did not differ from XX females in the studied mating characteristics. Similarly. deviation in the Y chromosome number affected sternopleural bristle number significantly in males but not in females as well as carrying with it an increased developmental instability with respect to intraindividual bristle frequencies. The effect of the differences in mating activity among males with different numbers of Y chromosomes is a strong stabilizing selection for the XYlXX sets of sex chromosomes. Literature cited k L U N D , S.-E. 1977. Mating behaviour as a fitness component in maintaining allozyme polymorphism in Drosophila rnelanogaster. 11. Selection in the leucine aminopeptidase-A allozyme system. -Hereditas 87:261-270 ASLUND, S.-E. and RASMUSON, M. 1976. Mating behaviour as a fitness component in maintaining allozyme polymorphism in Drosophila melanogaster. -Hereditas 82: 175-178 BARIGOW. C. 1951. The iduence of the Ychromosome on quantitative characters of D. melanogaster. -Heredity 5: 4 IS432 254 s.-E. ASLUND ET AI.. Hereditas 89 (1978) COOPER. K. W. 1956. Phenotypic effects of Y chromosome hyperploidy in Drosophila melanogaster. and their relation to variegation. -Genetic.s 4/:242-264 GOLDSMITH, R. B . . HANNAH. A. and PITERNICK, L. 19S1. The podoptera effect in Drosophila melanogastrr. -Univ. Culif (Berkc4ey) Publ. Zool. SS:67-294 KFARSFY. M. J. and KOJIMA. K. 1%7. The genetic architeclecture of body weight and egg hatchability in Drosophila melanogastrr. -Generics S6:23-37 KIEFER. B. J. 1%8. Dosage regulation of ribosomal D N A in Drosophilu melanogaster. -Pror. Nut. Arad. Sci. USA 6/:8569 MATHER, K. 1944. The genetical activity of heterochrornatin. -Proc. Roy. Soc. Lond. B /32:309-332 SPOFFORD, J . B. 1976. Position effect-variegation in D wsophila. -In Thr Genetics und Biology of Drosophir'u, I' d l r (Eds. M. ASHBURNER and E. NOVITSKI), Academic Press, London TARTOF, K. D. 1971. Increasing the multiplicity of ribosomal RNA genes in Drosophika melanoga.sti3r. -Science 171: 294-297 WILLIAMSON. J. H . 1976. The genetics of the Y chromosome. -