A Further Study on Induction of Functional Sex Reversal in Genotypic Males of the Medaka (Oryzias Latipes) and Progenies of Sex Reversals.

ESPITE a great deal of work on artificial control of gonadal sex differentiaD t i o n in every class of vertebrates, functional sex reversal induced by administration of sex hormones has rarely been achieved. Complete and functional sex reversal in genetic males under the influence of estrogens (either estrone or stilbestrol) was successful in a cyprinodont fish, the medaka (Oryzr" Zatipes) . Induced sex reversals of genetic males in mating with normal males produced viable offspring (YAMAMOTO 1953). GALLIEN (1954a,b j demonstrated that functional sex reversal in genetic males of the newt (PZeurodeZes waltlii) can be induced by estradiol benzoate. GALLIEN (1955, 1956) and CHANG and WITSCHI (1955) succeeded in inducing functional sex reversal in genetic males of the clawed toad (Xenopus Zaevis) by treatment with estradiol. In both the newt and the clawed toad, progenies of sex reversals by normal males were only males, indicating that the female is heterogametic (WZ) and the male homogametic (ZZ). In amphibians and higher vertebrates, however, functional sex reversal from female to male by administration of male sex hormone had not heretofore been achieved. I n the medaka, induction of functional sex reversal in genetic females under the influence of methyl testosterone was also successfully accomplished (YAMAMOTO 1958). In an oviparous cyprinodont, the medaka (Oryzins Zatipes) in which the sexdetermining mechanism is XX for female and XY for male, either the gene R (orange-red) or r (white) is borne by the X or Y chromosomes (ALDA 1921 j . When a white female (X'X'j is mated with a heterozygous orange-red male (XrYR), the progeny are white females (X'X'j and orange-red males (XrYR) in equal numbers. In matings of this sort, white ( r ) fish are females and orange-red ( R ) are males because the gene R for a dominant orange-red condition is located only in the Y chromosome. Hence the r and R can be used as markers of sex genotypes XX and XY. The father-to-son inheritance is always displayed except in rare exceptional fish in which the R gene dissociates itself from the sex-limited inheritance. Since the