16 



BIOLOGIC BASIS OF SEX 



3rd chromosome. The location of this allele, 

 tra, is at 44 to 45 or between the genes scar- 

 let and clipped. When homozygous the gene 

 transformed diploid females into sterile 

 males. Heterozygotes showed no detectable 

 differences from normal females of XX con- 

 stitution. Males XY homozygous for tra 

 or heterozygous for it were indistinguish- 

 able from normal males. The homozygotes 

 XX, tra/tra were female in body size, but 

 otherwise were nearly male in appearance. 

 They had fully developed sex combs, male 

 colored abdomens, normal male abdominal 

 tergites, anal plates, external genitalia, 

 genital ducts, sperm pumps, paragonia, and 

 showed the usual rotation of the genital and 

 anal segments through 360 degrees. They 

 mated with females readily and normally. 

 The testes, however, although normal in 

 color, elongated, curved, and attached to 

 the ducts were of small size. Testis size was 

 never that found in normal brothers. The 

 addition of a single Y or two Y's did not 

 alter fertility. 



The triploid females 3X + 3A homozy- 

 gous for tra, had large bodies, ommatidia 

 and wing cells. They resembled the diploid 

 homozygous tra individuals in having male 

 external genitalia, well developed ejacula- 

 tory ducts, sperm pumps, and accessory 

 glands, testes elongated but narrower than 

 those of normal males, and sex combs aver- 

 aging about 9.6 teeth. They mated with fe- 

 males but were completely sterile. 



Triploids with one or two doses of tra 

 were like wild type triploids in having no 

 sex combs and being female throughout. In- 

 tersexes having one or two doses of tra were 

 similar to intersexes having only wild type 

 genes in the locus. 



Sturtevant obtained one superfemale 

 which was homozygous for tra. It had male 

 genitalia and sex combs with only about 

 half the normal number of teeth. This in- 

 dividual argues for a greater balance to- 

 ward the female side of sexual development 

 than either the diploid or triploid females 

 previously discussed. The evidence is, how- 

 ever, contradictory to that furnished by the 

 Hr gene as indicated earlier. 



A combination of two or more genes, 

 Beaded and various Minutes, having well 

 known phcnotypic effects, has sometimes 



produced phenotypes which have been in- 

 terpreted as peculiar, low grade types of 

 intersexuality in males (Goldschmidt, 

 1948, 1949 and 1951). The data showed that 

 the Beaded cytoplasm favors the low grade 

 intersexual male whereas the Minute cyto- 

 plasm favors the reduced male with the 

 hetcrozygote being intermediate. Just how 

 far these types may be related to the other 

 types strongly affected by specific genes is 

 a matter of question, having at least other 

 interpretations (Sturtevant, 1949). 



In 1950, Milani trapped an inseminated 

 female of D. subobscura w^iich segregated 

 intersexual progenies. Spurway and Hal- 

 dane (1954) studied these intersexual 

 types. A recessive guiding development to- 

 ward these intersexes was located on the 5th 

 chromosome of subobscura. When present 

 it caused the XX homozygous females, 

 ix/ix + 2A, to have sex combs on both the 

 first and second tarsal joints. The numbers 

 of teeth making up the sex combs w^ere re- 

 duced as also were the sizes of the teeth. 

 The illustration in Spurway and Haldane's 

 (1954) paper indicates that the number of 

 teeth was 7 on the first tarsal joint and 5 

 on the second joint, whereas the sex combs 

 of the males had 11 teeth on the first joint 

 and 9 on the second. A series of changes 

 were observed in the genital plates which 

 graded from those resembling true females 

 to those approaching the male type. 



C. OTHER CHROMOSOME GROUP ASSOCIATIONS I 



DROSOPHILA AMERICANA 



I), aniericana has 4 chromosomes in the 

 female genome and 5 chromosomes in the 

 male genome. As compared with D. virilis 

 the X chromosome is fused with the 4th 

 chromosome and the 2nd chromosome is 

 fused with the 3rd, the 5th and 6th chromo- 

 somes are free in the female, whereas in the 

 male genome the Y chromosome, 4th, 5th 

 and 6th chromosomes are free and the 2nd 

 and 3rd fused. Stalker (1942) has shown 

 that the three female genomes are balanced 

 and lead to triploid females as they do in 



D. melanogaster. D. aniericana triploids 

 differ from their diploid sisters in having 

 bigger ommatidia, larger wing cells and 

 somewhat larger bodies. When these trip- 

 loids are bred to diploid males they give 



