IS THERE A GENE REGULATING THE SCUTE LOCUS ON THE THIRD CHROMOSOME OF D. MELANOGASTER?

J. M. Rendel ¹

¹ C.S.I.R.O., Division of Animal Genetics, P.O. Box 90, Epping, 2121, N.S.W., Australia

A section of the third chromosome of D. melanogaster some 25 to 40 centimorgans long including sr was transferred from a wild-type stock selected by Latter for high scutellar bristle number into a scute stock with a large number of scutellar bristles. This segment is shown to have a large effect on the bristle numbers of wild-type flies, to reduce the strength of canalization of the scute phenotype at 4 bristles, to have little, if any, effect on bristle numbers of scute flies with less than 4 bristles but to increase the number of flies with 5 and 6 scutellar bristles in scute stocks that normally have a large number of flies with 4 bristles. It is suggested that this segment in unselected chromosomes contains a gene that regulates bristle number by repressing the scute locus and that Latter has selected a mutant of the regulator which fails to repress the action of the scute locus.