Correlated response in scutellar bristles to selection for abdominal bristles in Drosophila melanogaster.

"DEL (1963) recently discussed the various ways in which genetic correlaR:ons may be generated. In particular he suggested that, when the development of two characters is dependent upon common resources (T), then it is reasonable to assume that a proportion ( a ) of T will be used to develop one character and the remaining proportion (1-a) will be used to develop the other character. Hence a and (1 -a) may be thought of as measures of the relative competitive abilities of the two characters. If this is the case then changes in T or in a or both could lead to a change in the genetic correlation between the two characters. From results of a selection experiment for scutellar bristles in DrosophiZa melanogaster, he found that the realised genetic correlation between the scutellar bristlaes and the abdominal bristles changed with different amounts of selection and in different genotypes. Using the assumption that the two bristle systems were sharing the same resources, he was able to show that such changes resulted from changes in both total resources and relative competitive abilities. In RENDEL'S experiment, selection was based on the scutellar bristles, mainly of the males carrying the scute mutant. As some abdominal bristle selection lines were available, the opportunity was taken to look at the realised genetic correlation in an alternative situation, where the direct selection had been for abdominals rather than for scutellars. This study is reported in the present paper.