50 



BIOLOGIC BASIS OF SEX 



otherwise indistinguishable male types. 

 With these characteristics the goat types 

 have remarkable advantages over other 

 species for the solution of problems of 

 hermaphroditism. 



The gene for goat hermaphroditism has 

 even more interest when it is contrasted 

 with that of another gene, tra, discovered 

 by Sturtevant (1945). Tra is recessive wdth 

 no distinguishable heterozygous effect. In 

 the homozygous state it converts the zygotic 

 female into a form with completely male 

 genitalia and internal reproductive tract 

 with no evidence of the female sexual repro- 

 ductive system. The gene effects in Dro- 

 sophila are more extreme than those in 

 goats but are concordant in showing that 

 there are loci in the autosomes which may 

 be occupied by recessive genes having direct 

 effects on phenotypic development of the 

 genotypic female. This evidence indicates 

 the significance of these genes rather than 

 the happenstance of their being in the 

 autosome, X or Y chromosome. 



B. SEX IN THE MOUSE 



The mouse has the XY + 38 A chromo- 

 somal arrangement for the males and XX + 

 38 A for the females. Similar karyotype pat- 

 terns have been reviewed for some Amphibia 

 and fish. Other Amphibia and fish may have 

 their karyotypes reversed as both forms are 

 found in nature or observed in breeding 

 studies. Similar reversals may be made ex- 

 perimentally in the phenotypes even though 

 the genotypes remain unaltered. Birds show 

 the sex differentiating arrangement of ZW 

 for the females and ZZ for the males. Par- 

 thenogenesis seems to lead to males of ZZ 

 type in domestic fowl and turkeys. In an 

 evolutionary sense the mammals could have 

 originated from and perpetuated either of 

 the major karyotype sex arrangements. 



Mice and men are alike in that the X has 

 female-determining properties and the Y 

 male potencies. How much part the genes in 

 the autosomes have in sex develojoment is 

 not yet clear. Welshons and Russell (1959) 

 have shown that mice of the presumed X() 

 constitution are females and arc fertile. 

 They have 39 as the modal number of 

 chromosomes found in their bone marrow 

 cells, wiiereas the genetically proven XX 

 types have 40 cln'omosomcs. X ('hroinosoinc- 



linked genes' behavior substantiate the 

 chromosomal constitutions of XO and XX 

 as females and XY as males. 



These results are further supported by the 

 breeding behavior of the X-linked recessive 

 gene, scurfy (Russell, Russell and Gower,. 

 1959). This gene is lethal to the hemizygous 

 males before breeding. The genetics of the 

 scurfy females have been analyzed by trans- 

 planting the ovaries to normal recipient fe- 

 males and obtaining offspring from them. In 

 the scurfy stock the XO type occurred as 0.9 

 per cent of the progeny. The YO progeny 

 w^ere not identified and probably die pre- 

 maturely. Nondisjunction of the X and Y 

 chromosomes in the males could result in 

 sperm carrying neither X nor Y chromo- 

 somes. These sperm on fertilization of the 

 X egg would give an XO + 2A type individ- 

 ual. Because the result is a female, this 

 would support the Y chromosome as of male 

 potency. The mouse arrangement may then 

 be expected to be like Melandrium in which 

 a well worked out series of types is known. 



Sex ratio in mice is strain dependent over 

 what has thus far proven to be a 10 to 15 

 per cent range. Weir (1958) has shown that 

 for two strains of mice established by select- 

 ing for low and high pH, the sex ratio figures 

 were 33 and 53 per cent for artificially in- 

 seminated mice and 41 and 52 per cent for 

 natural matings of these respective strains. 

 The differential pH values for the bloods of 

 the low line were 7.498 ± 0.006 and for the 

 high line 7.557 ± 0.007 as of the sixth 

 generation of selection. The parents with 

 the more alkaline bloods tended to have 

 greater percentages of males in their prog- 

 enies. These results direct attention to the 

 genotype dependent phenotypic factor 

 which may be of some importance for 

 variations in sex ratios. 



C. SEX AND STERILITY IN THE CAT 



The tortoiseshell male cat has long inter- 

 ested geneticists because it has seemed that 

 by theory it should not be. However, nature 

 has wonderful ways of circumventing best 

 laid hypotheses, sometimes when they are 

 fals(\ sometimes when they have not been 

 probed dee])ly enough. The yellow gene for 

 coat color in cats is sex-linked. This gene 

 operates on an autosomal background of 

 ^(■lu's for black oi' tabby. Tlu^ females may 



