A Search for Sex Genes I N T H E Second Chromo- Triploid Method

HE male determining influence of the autosomes on sex differentiation T in Drosophila melanogaster was proven by BRIDGES in 1921 with the discovery of triploid intersexes. He found that individuals with two X chromosomes, as in diploid females, and three of each autosome (3A) develop intersexually. BRIDGES concluded that sex is determined by an interplay of female determining genes located principally in the X chromosome and male determining genes located principally in the autosomes. The question of a single sex gene versus multiple sex genes in the X chromosome of Drosophila melanogaster was debated by investigators for a number of years. PATTERSON, with his gynandromorph experiments in 1931, restricted a possible female determining sex factor to the garnet-forked region of the X chromosome. I n later experiments, using hyperdiploid males; i.e., those carrying in excess a short fragment of the X chromosome, PATTERSON, STONE and BEDICHEK (1937) eliminated all regions of the X chromosome as a possible site of a primary female sex gene except the wavy-garnet region. I n 1938, PATTERSON narrowed this region to the garnet-pleated section, between salivary gland bands 13 A2 and 13 A6. Males hyperploid for this region failed to live. MULLER (1930) and DOBZHANSKY and SCHULTZ (1934) made observations on certain diploid aneuploids with regard to presence of a possible female sex gene(s) in the X chromosome. In 1934 DOBZHANSKY and SCHULTZ presented results of their studies of sex balance in certain sections of the X chromosome. They crossed hyperdiploid males and also X,4 translocation males to triploids homozygous for recessive X chromosome marker genes. This method, originally suggested by MULLER and STONE (1930), allowed the authors to observe the effects of adding extra fragments of the X chromosome to the intersex chromosome complement (2X3A). DOBZHAKSKY and SCHULTZ showed that the addition of certain long fragments of the X chromosome to the 2X3A intersex complement resulted in hypotriploid females of reduced fertility. The shortest section which nevertheless produced a weakly fertile hypotriploid female when added to the 2X3A chromosome set was duplication L.V.M., a section covering the y-pn plus ju-bb regions. Very short sections from the extreme left as well as very short sections including both right and left ends of the X chromosome produced slight shifts in the mean sex type of the duplication intersexes in the female direction. PIPKIN (1940) studied different duplication intersexes possessing 2X3A and a short section of each region of the X chromosome. Small shifts of sex type SOME OF DROSOPHILA MELANOGASTER USING T H E