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  Section: Genetics » Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting
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Triploid intersexes in Drosophila and genie balance theory

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 presence of triploid intersexes in the experiment conducted by Bridges (Fig. 17.3) is a definite proof that autosomes also carry factors for sex determination. These intersexes are sterile individuals, which are intermediate between male and female. The results, where intersexes, supermales and superfemales were obtained, were interpreted by Bridges in the form of Genie Balance Theory of Sex Determination. According to this theory, ratio between the number of X-chromosomes and number of complete sets of autosomes will determine the sex. The X-chromosome is believed to carry female tendency genes, while autosomes carry male tendency genes. Both these sets of genes start functioning and there has to be a balance between them for an individual to become male or female. In one complete set of chromosomes (A + X), female tendency genes are more. Consequently if ratio between X and A is 1.0, it will be a female individual. The different ratios between number of X chromosomes and the number of A's, i.e. sets of autosomes (X/A) and their corresponding phenotypes for sex are shown in Table 17.2 and summarised in Table 17.3.

genteic botany

genteic botany

As shown in Table 17.2, when X/A ratio is 1.0, the individual will be female and when it is 0.5, it would be male. When this balance is disturbed, the individual deviates from normal male or normal female. For instance, when the ratio (X/A) falls between 1.0 and 0.50, it would be intersex; when below 0.50, it would be supermale and when above 1.0 it would be superfemale (Table 17.3).

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