Evidence for Genetic Homology between Chromosomes I and IV in Drosophila Melanogaster, with a Proposed Explanation for the Crowding Effect in Triploids.

ROM a consideration of chromosome evolution in Drosophila, it has been suggested F (MULLER and PAINTER 1932) that in the basal heterochromatin, regions of genetic homology might exist between all of the chromosomes in D. melanogaster. In a cytological study of the chromocenter in salivary gland nuclei, PROKOFYEVA (1935) describes connections (which she interprets to be conjugations of homologous loci) between all of the chromosomes in the proximal heterochromatic regions. Other workers have also suggested a meiotic relationship between non-homologous chromosomes (SCHULTZ 1951 ; LINDSLEY 1955). Genetic evidence for homology specifically between the X chromosome and chromosome IV has been reported by GERSHENSON (1940), LINDSLEY and NOVITSKI (1953), and PARKER (1954). Further evidence for genetic homology between the X chromosome and chromosome IV is presented below. It will be shown, in addition, that the expectations from triploid females based upon assuming a general homology between all of the chromosomes (the homology between homologous chromosomes being much stronger than that between non-homologous chromosomes) are realized experimentally (BRIDGES and ANDERSON 1926; BEADLE 1935) and that, therefore, general homology between the chromosomes of Drosophila would account for the observed “crowding effect” in triploids.