Genetic control of morphogenetic variation in the sexcombs of drosophila melanogaster

Abstract

The effect of the Y-chromosome on the sexcombs in the legs of Drosophila melanogaster has been examined in four different genotypes, viz., Oregon R+, y, sx and Pc-Scx. For this purpose, various Y-chromosome-fragments (Y^L and Y^S) and one or two XO conditions have been used. The results of this investigation show that both long (Y^L) and short (Y^S) arms of the Y-chromosome tend to increase the teeth number in the sexcomb of the first legs in all genotypes excepty. The XO-1 condition, derived by the loss of one X, appears to decrease it; the XO-2, resulting from the fertilization of an X-bearing ovum by a nullo-Y sperm, appears to show an increased teeth number or no effect at all. The effect of Y-fragments is least in the case of y and maximum in sx. The various Y-fragments used also show a parallel, though inversely related, effect on the production of intermediate bristles in sx. These Y-fragments show an opposite effect on the sexcombs of the second and third legs of the Pc-Scx genotype. Here the mean numbers of teeth are significantly reduced in all cases as compared to those in XY; Pc-Scx/++ genotype. The different Y-fragments behave differently in their effect on sexcomb pattern. It has been suggested that secondary modifiers may be present in association with different genotypes as well as in the Y, which are required to maintain a morphodynamic equilibrium in pattern formation.