X/A ratio and gynandromorphs 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


In Drosophila, occasionally flies are obtained which have female characters in one part of body and male characters in the remaining parts (Fig. 17.4). Such individuals are known as gynandromorphs and are believed to result due to loss of an X-chromosome in particular cell during development. If this event happens during first mitotic division of zygote, then one of the two cells of two celled proembryo will have 2A + XX with X/A =1.0 and the other cell will have 2A + X with X/A = 0.5 (Fig. 17.5). The fly derived from such a situation will have half of its body as female and the other half as male. Availability of gynandromorphs and their cytological examination suggested that Y-chromosome does not play any role in determination of sex in Drosophila.


Loss of an X-chromosome during mitosis in a 2A + XX cell, leading to the derivation of two daughter cells, one having 2A + XX and the other having 2A + X.
Fig. 17.5. Loss of an X-chromosome during mitosis in a 2A + XX cell, leading to the derivation of two daughter cells, one having 2A + XX and the other having 2A + X.
 
A gynandromorph fruitfly (Drosophila melanogaster)showing female and male parts.
Fig. 17.4. A gynandromorph fruitfly (Drosophila melanogaster)showing female and male parts.

Sexual dimorphism in Drosophila melanogaster and Coenorhabditis elegans; in Drosophila, body size, abdominal pigmentation and sex comb on the foreleg are major external features for differentiating two sexes; in C. elegans, presence of copulatory organs in the tail of male, presence of two armed gonads in hermdphrodite (one armed in male) and larger size of the hermaphrodite are used for differentiating the two forms (modified from Hodgkin, 1990).
Fig. 17.6. Sexual dimorphism in Drosophila melanogaster and Coenorhabditis elegans; in Drosophila, body size, abdominal pigmentation and sex comb on the foreleg are major external features for differentiating two sexes; in C. elegans, presence of copulatory organs in the tail of male, presence of two armed gonads in hermdphrodite (one armed in male) and larger size of the hermaphrodite are used for differentiating the two forms (modified from Hodgkin, 1990).