The Relation of Repeats to Position Effect in Drosophila Melanogaster

In Drosophila melanogaster it has been established that the action of at least some genes is affected by their position in the chromosomes. Critical evidence for this phenomenon of position effect has been given by Sturtevant (1925), Dubinin and Sidorow (1935), and Panshin (1935). Position effects have been detected only in cases in which the relative position of a gene with respect to its neighbors has been altered by a chromosomal rearrangement. It is conceivable that the effective position of a gene may also be changed as a result of a substitution in an adjacent gene of one allele by another. Such a possibility was put to experimental test by Sturtevant (1928) for the dominant mutants, Delta (Dl) and Hairless (H), three units apart in the third chromosome; however, no difference could be demonstrated between Dl H/++ and Dl+/+H.