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  Section: Genetics » Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting
 
 
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Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting

 
     
 
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Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting
Chromosome Theory of Sex Determination 
Balance Theory of Sex Determination X/A ratio in Drosophila
Triploid intersexes in Drosophila and genie balance theory
X/A ratio and gynandromorphs in Drosophila
X/A ratio in Coenorhabditis elegans (a free living nematode)
Balance Between Male and Female Factors
- Diploid intersexes in gypsy moth (Lymantria)
- X/A ratio and multiple numerator elements (Drosophila and Coenorhabditis)
Sex Determination in Plants
Methods for determining heterogametic sex in plants
Sex determination in Coccinia and Melandrium
Sex determination in other dioecious plants
Sex Chromosomes in Mammals Including Humans (Homo sapiens)
TDF, ZFY and SRY genes in humans
H-Y antigen and male development in mammals
Single gene control of sex
Sex determination in Asparagus
Tassel seed (ts) and silkless (sk) genes in maize
Transformer gene (tra)in Drosophila
Haploid males in Hymenoptera
Hormonal control of sex
Environmental Sex Determination in Reptiles
Dosage Compensation in Organisms with Heterogametic Males
X-chromosome inactivation in mammals
Position effect variegation
Hyperactivity of X-chromosome in male Drosophila
Lack of Dosage Compensation in Organisms with Heterogametic Females
Genetic imprinting
Sex determination in most plants and animals is concerned with the study of factors which are responsible for making an individual male, female or a hermaphrodite. For many years in the past, the sex determination mechanisms were explained purely on the basis of sex chromosomes, trje constitution of which generally differed in male and female individuals. In recent years, however, a distinction has been made firstly, between sex determination and sex differentiation and secondly, between the roles played by the chromosome constitution and specific genes (located both on sex chromosomes and autosomes) in achieving sexual dimorphism. It has been shown that sex determination is a mere signal initiating male or female development patterns, and that sex differentiation involves the actual pathway of events leading to the development of not only male and female organs but also the secondary sex characters (Fig. 17.1).
As a part of studies of the general problem of differentiation during development, sexual dimorphism has also been studied in considerable detail in atleast two organisms i.e. Drosophila melanogaster (fruitfly) and Coenorhabditis elegans (a free living nematode). In both these species cytogenetic, genetic and molecular approaches, have been used, to understand the mechanism of sex determination and sex differentiation. Many mutants with altered sexual phenotypes have been generated, permitting identification of key regulatory genes. Several of these genes have also been cloned and their gene products examined yielding detailed information about the mechanism involved at the molecular level. Considerable progress has also been made in understanding the mechanism of sex determination in humans, mouse and other mammals. In these cases also, new genes have been identified, isolated and cloned to know in detail the mechanism at the molecular level. These different aspects along with the present state of our knowledge of sex determination in plants and animals will form the outline of this section.

Three stages of the development and differentiation of sex, involving the primary signal and the two sets of genes (sex determining and sex differentiation genes).
Fig. 17.1. Three stages of the development and differentiation of sex, involving the primary signal and the two sets of genes (sex determining and sex differentiation genes).

 
     
 
 
     




     
 
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