FOUNDATIONS FOR SEX 



47 



reversed mothers XY, to normal males XY, 

 resulted in progenies containing 1 female to 

 2.2 to 2.4 males where the expected theoretic 

 relation would be 1 female to 3 males. The 

 male progenies were submitted to test 

 crosses. It was shown that the YY individ- 

 uals were, as expected, males. With the re- 

 moval of hormone feeding the normal sex- 

 determining mechanism reestablished itself 

 as XX for the female and XY for the male in 

 the following generation. The hormone feed- 

 ing had apparently, through its excess fe- 

 male-stimulating growth capacities, caused 

 the somatic tract of the fish to develop 

 throughout as a female l)ut did not in any 

 way influence the fundamental genetic con- 

 stitution of the cells. In at least one case 

 (1957j, Yamamoto has shown that true in- 

 tersexes can be produced having the geno- 

 type XY. The secondary sex characters were 

 intermediate between both sexes. The gonads 

 became ovotestes, testicular elements in the 

 anterior and ovarian components in the pos- 

 terior region. By use of the same technique, 

 but substituting methyl testosterone as the 

 hormonal additive to the diet at the begin- 

 ning of the indifferent gonad stage and con- 

 tinuing through sex differentiation, it has 

 been possible where quantities of 50 ;ag. per 

 gm. diet were fed in the diet to cause both 

 genetic sexes XX or XY to differentiate into 

 males with rudimentary testes which even- 

 tually become neuters on becoming full- 

 grown fish. Intermediate dosages resulted 

 in XX individuals becoming males and 

 in 3 cases intersexes. These phenotypic 

 males of the XX type became fertile, 

 ])roducing spermatozoa which on fer- 

 tilization of eggs of normal females gave 

 all female progeny. Again the effect of 

 the sex hormone was temporary in that 

 only the treated generations showed the sex 

 reversal, their progeny returning to the 

 customary XX female and XY male types. 

 Sex reversals have been accomplished on 

 fish that were themselves progeny of sex- 

 reversed parents. Genetic analyses showed 

 that the sex-reversed males were all XY 

 genotypes rather than YY genotypes. This 

 was accounted for through the low viability 

 of the males of the YY genotype. 



These observations are similar to those 

 observed in some of the Amphibia and are 

 also of interest in connection with the regu- 



lar sex mechanisms which have developed 

 for Sciara or for those of occasional abnor- 

 mal types as those observed in Drosophila 

 and man. These cases make it evident that 

 phenotypic sex may be derived in a quite 

 different manner from that adduced by the 

 sex promoting genes carried through the 

 germ line, even though the germ line may 

 be nourished by the products of the pheno- 

 typic somatic cells. The time in development 

 when the presence of hormone in excess of 

 and external to the organism's own gene 

 initiated sex organizers, if it is to be ef- 

 fective, would seem to be important. The 

 brief embryonic stage before the determi- 

 native changes in sex primordia have oc- 

 curred, the neutral stage or stage of bisexual 

 potentiality, is likely to be most influenced 

 by external agencies that redirect sex dif- 

 ferentiation. Developraentally speaking, 

 this period is rather short for the primary 

 sex organs, although possibly longer in 

 terms of some secondary sex characters such 

 as the breasts in man. 



IX. Sex and Parthenogenesis in Birds 



Sex in birds follows the general ZW -|- 

 2A for the female and ZZ + 2A for 

 the male; sex-linked genes follow this 

 pattern. Although breeding results in gen- 

 eral follow expected orthodox lines, the 

 birds are subject to much mosaic variation 

 in their color patterns as well as significant 

 sterility relations in species hybrids. Sec- 

 torial mosaics are prominent. Some of these 

 can be accounted for by nondisjunction, 

 polyspermy, binucleate eggs fertilized by 

 difi"erent sperm, development of super- 

 numerary sperm and other known genetic 

 means, whereas others still lack adequate 

 information. Gynandromorphs have been 

 described, but are subject to question in 

 view of the plumage characteristics observed 

 in mosaics and because of the fact that the 

 sex hormones are such that striking plumage 

 differentiations may occur if for any reason, 

 for instance disease, the hormone-producing 

 organs are removed from the birds. In 

 ordinary fowl the ovary produces hormones 

 which suppress male plumage, whereas in 

 the seabright male a gene controlled change 

 in the testis has taken over this functional 

 attribute. Mottling and flecking are also 

 common, particularly in the plumage pat- 



