294
L. G A L L I E N
nephros (Gallien, 1954) and the limbs (Collenot, 1965). All these facts
provide evidence that these hormones can affect development in all its
aspects.
5. Sex Reversal in Teleosts
Complete, permanent, functional reversal of the sexual phenotype of the
gonads has been obtained by Yamamoto (1953, 1955, 1958, 1959, 1963) in
Oryzias latipes. The administration of estradiol to the larvae produces
100% females, while methyltestosterone results in testicular differentiation
of the gonads. The acquired differentiation appears to be stable and sexreversed individuals can reproduce. The particular interest in Yamamoto's
experiments rests in the fact that the genetic analysis of the offspring of
these sex-reversed fish has been carefully documented. Actually, in Oryzias
there are genetic markers, sexlinked, that have made it possible to establish
theXX 9 iXYci* constitution of this species (Aida, 1921). From the crosses
made by Yamamoto, with X and Y chromosomes marked, the chromosomal
makeup of the offspring and the origin of the sex chromosomes could be
verified. Thus a direct measurement of the genetic constitution is added
to the statistical data.
B. Relationship between Genetic Constitution
and Sexual Organogenesis
1. Functional Sex Reversal and Genetic Constitution
In a limited number of cases, in amphibians and the teleost, 0. latipes,
physiologically functional individuals of sexually reversed phenotype have
been obtained (neomales and neofemales). This reversal of sex has occurred
as a result of either the action of steroid hormones or the grafting of presumptive gonadal areas or differentiated gonads. As a consequence of this
situation, two individuals of the same genetic sex can be crossed, and by
analysis of the offspring, the genetic constitution of sex in the species
studied can be determined. Various combinations that might be anticipated
to result in sex reversal have been made (Table III).
The accumulated results obtained in amphibians and 0. latipes support
the following general conclusions: (1) Sex reversal assumes a bisexual
genetic constitution of sex. (2) For a given species sex is homoheterogametic
in nature. (3) In amphibians two modes of sex determination are represented: Homogametie male (ZZ)-heterogametic female (ZW), exemplified
by Ambystoma, Pleurodeles, and Xenopus, and homogametie female (XX)heterogametic male (XY), as in Ranidae. (4) The sexual form of the gametes
(spermatozoa and oocytes) is not a necessary consequence of the genotype
of the gonia, but rather is a result of the gonadal area in which they develop.
This emphasizes the role in organogenesis of the cortex and the medulla of
L. G A L L I E N
nephros (Gallien, 1954) and the limbs (Collenot, 1965). All these facts
provide evidence that these hormones can affect development in all its
aspects.
5. Sex Reversal in Teleosts
Complete, permanent, functional reversal of the sexual phenotype of the
gonads has been obtained by Yamamoto (1953, 1955, 1958, 1959, 1963) in
Oryzias latipes. The administration of estradiol to the larvae produces
100% females, while methyltestosterone results in testicular differentiation
of the gonads. The acquired differentiation appears to be stable and sexreversed individuals can reproduce. The particular interest in Yamamoto's
experiments rests in the fact that the genetic analysis of the offspring of
these sex-reversed fish has been carefully documented. Actually, in Oryzias
there are genetic markers, sexlinked, that have made it possible to establish
theXX 9 iXYci* constitution of this species (Aida, 1921). From the crosses
made by Yamamoto, with X and Y chromosomes marked, the chromosomal
makeup of the offspring and the origin of the sex chromosomes could be
verified. Thus a direct measurement of the genetic constitution is added
to the statistical data.
B. Relationship between Genetic Constitution
and Sexual Organogenesis
1. Functional Sex Reversal and Genetic Constitution
In a limited number of cases, in amphibians and the teleost, 0. latipes,
physiologically functional individuals of sexually reversed phenotype have
been obtained (neomales and neofemales). This reversal of sex has occurred
as a result of either the action of steroid hormones or the grafting of presumptive gonadal areas or differentiated gonads. As a consequence of this
situation, two individuals of the same genetic sex can be crossed, and by
analysis of the offspring, the genetic constitution of sex in the species
studied can be determined. Various combinations that might be anticipated
to result in sex reversal have been made (Table III).
The accumulated results obtained in amphibians and 0. latipes support
the following general conclusions: (1) Sex reversal assumes a bisexual
genetic constitution of sex. (2) For a given species sex is homoheterogametic
in nature. (3) In amphibians two modes of sex determination are represented: Homogametie male (ZZ)-heterogametic female (ZW), exemplified
by Ambystoma, Pleurodeles, and Xenopus, and homogametie female (XX)heterogametic male (XY), as in Ranidae. (4) The sexual form of the gametes
(spermatozoa and oocytes) is not a necessary consequence of the genotype
of the gonia, but rather is a result of the gonadal area in which they develop.
This emphasizes the role in organogenesis of the cortex and the medulla of