260
L. G A L L I E N
necessary for differentiation in both the male (M) and the female (F)
directions. On this common structure, a genetic dissymmetry is imposed,
the homoheterogametic sexual constitution. A genie balance exists between
the sum of the M factors and the sum of the F factors. This assures the final
dominance of one of the groups of genes influencing sex. In the most favorable situations, this dissymmetry can be observed cytologically owing to
the presence of sex chromosomes. The genetic basis of sex is established at
the time of fertilization. Thus the genetic determination of sex is syngamic.
Heteroploidy, the production of mutations affecting the genes influencing sex, allows for modification of the genetic foundation and the analysis of
its consequences.
B. Intrinsic Epigenetic Factors in Sexual Organogenesis
These factors arise in the course of ontogenesis. They are essentially
systems of enzymes, inductive substances, and hormones that are manifested at various stages in the course of development. They are the expression of the genetic constitution.
C. Extrinsic Epigenetic Factors in Sexual Organogenesis
These are the factors in the environment. They can conceal or dominate,
either temporarily or permanently, the expression of the genetic sex of the
individual. With their maximum influence, they bring about the phenotypic
reversal of sex, with the genetic constitution remaining unchanged. Along
with general environmental factors such as temperature, other factors have
proved to present a useful method of analysis. These include teratogenic
agents, hormones introduced into the metabolic cycles, surgical interventions (isolations, deficiencies, recombinations) accomplished in grafts, and
cultures in vivo or in vitro. The operation of these factors, in disturbance of
the normal development, has been one of the methods of arriving at an
understanding of the mechanisms taking place in sexual differentiation.
It was at the beginning of the century with the work of McClung (1902),
Castle (1903), Wilson (1905, 1906), and Correns (1907) on the genetic
constitution of sex, and that of Bouin and Ancel (1904a,b), Baltzer (1914),
Lillie (1916, 1917), and Keller and Tandler (1916) on hormonal factors
occurring in the embryonic differentiation of sex, that the analysis of the
causes of sexual organogenesis was undertaken in its modern form. Since
then the problem has been posed in terms of its basic implications : genetic
control, embryologie foundations, hormonal mediators, the role of the
environment.
This article will be limited to recent work on the role of epigenetic factors
in sexual organogenesis, with mention of their relationship to the genetic
constitution of the organisms. A general review of these questions has been
the object of several previous works: Ponse (1949); Witschi (1950, 1957,
L. G A L L I E N
necessary for differentiation in both the male (M) and the female (F)
directions. On this common structure, a genetic dissymmetry is imposed,
the homoheterogametic sexual constitution. A genie balance exists between
the sum of the M factors and the sum of the F factors. This assures the final
dominance of one of the groups of genes influencing sex. In the most favorable situations, this dissymmetry can be observed cytologically owing to
the presence of sex chromosomes. The genetic basis of sex is established at
the time of fertilization. Thus the genetic determination of sex is syngamic.
Heteroploidy, the production of mutations affecting the genes influencing sex, allows for modification of the genetic foundation and the analysis of
its consequences.
B. Intrinsic Epigenetic Factors in Sexual Organogenesis
These factors arise in the course of ontogenesis. They are essentially
systems of enzymes, inductive substances, and hormones that are manifested at various stages in the course of development. They are the expression of the genetic constitution.
C. Extrinsic Epigenetic Factors in Sexual Organogenesis
These are the factors in the environment. They can conceal or dominate,
either temporarily or permanently, the expression of the genetic sex of the
individual. With their maximum influence, they bring about the phenotypic
reversal of sex, with the genetic constitution remaining unchanged. Along
with general environmental factors such as temperature, other factors have
proved to present a useful method of analysis. These include teratogenic
agents, hormones introduced into the metabolic cycles, surgical interventions (isolations, deficiencies, recombinations) accomplished in grafts, and
cultures in vivo or in vitro. The operation of these factors, in disturbance of
the normal development, has been one of the methods of arriving at an
understanding of the mechanisms taking place in sexual differentiation.
It was at the beginning of the century with the work of McClung (1902),
Castle (1903), Wilson (1905, 1906), and Correns (1907) on the genetic
constitution of sex, and that of Bouin and Ancel (1904a,b), Baltzer (1914),
Lillie (1916, 1917), and Keller and Tandler (1916) on hormonal factors
occurring in the embryonic differentiation of sex, that the analysis of the
causes of sexual organogenesis was undertaken in its modern form. Since
then the problem has been posed in terms of its basic implications : genetic
control, embryologie foundations, hormonal mediators, the role of the
environment.
This article will be limited to recent work on the role of epigenetic factors
in sexual organogenesis, with mention of their relationship to the genetic
constitution of the organisms. A general review of these questions has been
the object of several previous works: Ponse (1949); Witschi (1950, 1957,