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  Section: Genetics » Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting
 
 
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Hormonal control of sex

 
     
 
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
A large number of case are known where sex is modified due to hormones secreted from sex organs. Three classical examples of hormonal or environmental control of sex would be presented here.

Sex in Bonellia
In Bonellia viridis, a marine worm, all larvae are genetically and cytologically similar. In this worm, male individual lives in the uterus of the female (Fig. 17.22). If a particular larva settles near proboscis of an adult female, it becomes a male individual, and lives in the uterus of the female. On the other hand, if it has to develop free in water, it becomes a female. Similarly, if a partly developed male is detached from the proboscis it become an intersex. Obviously the proboscis secretes a substance suppressing femaleness.

The Crew's hen
A case of complete sex reversal was reported in 1923 by Crew, where a fertile female fowl (hen), which had already produced offspring, changed over to a fully fertile male (cock). This resulted due to a damaged ovary in the female. It is believed that ovary in female secreted a male suppressing hormone. Therefore, in absence of ovary, testis could develop.

The Free-Martin
In cattle, when twins are produced, one of them being male and other female, female is sterile and male is normal. These are known as Free-Martin after the name of the worker, and would be produced only when there is a vascular connection between two embryos. The hormone perhaps suppresses the development of ovary in female.

 
     
 
 
     




     
 
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