FUNCTIONAL SEX-REVERSAL IN GENETIC FEMALES OF XENOPUS LAEVIS, INDUCED BY IMPLANTED TESTES.

Abstract

IN his thesis, CHANG (1953) reports that testes implanted into female larvae of the frog Xenopus suppress ovarian development, and that initial cortical inhibition sometimes is followed by testicular differentiation of one or several gonomeres. These experiments have been taken up again with the aim of studying the morphologic effects induced by testicular implants, the sexual behavior of converts, their reproductive capacity, and their genetic constitution. Regarding the last point, it is already known that ordinary female larvae are heterozygous with respect to sex-determining genes. Proof of this has been obtained from breeding experiments (CHANG and WITSCHI 1955a, 1956; GALLIEN 1955,1956). Recently reported cytologic evidence confirms that Xenopus belongs to the ZZ = male and ZW = female chromosomal type ( WEILER and OHNO 1962). Foremost remains the question whether the testicular nodes of sex-reversed females retain the ZW constitution, or assume a new one. The latter alternative could conceivably arise through migration of germ cells from the implant to the larval gonads or by chromosomal modifications. The observational material is not yet large enough to certify statistically that sex-reversal through testis implantation has occurred in CHANG’S or in our own experiments. Obviously, unequivocal evidence can be obtained only by breeding tests, such as will be described in the following pages. By raising experimental animals to the age of maturity, mating behavior and fertility of sex-reversed animals may also be studied.