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  Section: Genetics » Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting
 
 
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Balance Theory of Sex Determination X/A ratio in Drosophila

 
     
 
Content
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


The experiment of Bridges mentioned above, though demonstrated that Y-chromosome is not important for determination of sex, it did not indicate whether X-chromosome alone determines the sex or if autosomes also play any role in the mechanism. Individuals could, however, be obtained, which had two X-chromosomes as in the normal female, but were intersexes. Each of these intersexes had an extra set of autosomes (A) indicating that autosomes play a definite role in determination of sex. In this connection, Bridges' experiments on intersexes and supersexes are of special importance. Bridges, as early as 1922, came across certain Drosophila individuals which were triploids and thus had three sets of chromosomes (3A + 3X). These triploid individuals were normal females and were crossed with diploid males (2A + XY). The results obtained from such a cross are shown in Figure 17.3. As is obvious, from such a cross, normal diploid males, triploid females, intersexes, supermales and superfemales were obtained. Chromosome constitution of these phenotypically different sexes had a definite bearing on the mechanism of sex determination, as explained in the next section.
 
Results obtained from a cross of a triploid (3A + XXX) ♀ fly, and a diploid ♂ (2A + XY) fly in Drosophila.
Fig. 17.3. Results obtained from a cross of a triploid (3A + XXX) ♀ fly, and a diploid ♂ (2A + XY) fly in Drosophila.

 
     
 
 
     




     
 
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