Genetics of sex determination: An overview

Abstract

This chapter provides an overview of the genetics of sex determination. The 20th century has seen the discovery of sex chromosomes and the rise of genetics. Whereas the early geneticists tended to concentrate on mutations, many of which gave rise to defective enzymes and easily recognizable phenotypes, recent advances in molecular genetics have led to the isolation of an increasing number of genes that are active in development, but whose mode of action is not yet understood. These genes tend to interact with others and with environmental factors and show a greater resemblance to that part of the genotype that has been referred to as “minor genes” than to “major genes” giving rise to discreet Mendelian ratios. Whereas the latter were the only genes that could be methodologically handled in classical genetics, molecular genetics has the methodology to identify genes whose phenotypic effects are much more dependent on genetic background and environmental factors. Because sex differentiation is a gradual process during which the embryo assumes either a male or a female phenotype, the understanding of this process is becoming modified as more experimental data become available.