Many animal taxa show frequent and rapid transitions between male heterogamety (XY) and female heterogamety (ZW). We develop a model showing how these transitions can be driven by sex-antagonistic selection. Sex-antagonistic selection acting on loci linked to a new sex-determination mutation can cause it to invade, but when acting on loci linked to the ancestral sex-determination gene will inhi...

those produced by x-irradiation, the above result and further experiments producing mutations with neutrons may lead to new conclusions regarding the interaction of radiation ions with genes and hence of the size and structure of the gene. It is interesting to note that the ratio of effectiveness (5 or 6 to 1) for the effects on mature sperm of neutron as compared with x-irradiation is comparab...

It was a population based cross sectional study done with the objective of comparing some parameters (attitude & practice) of gender discrimination (GD) in rural and urban areas of Ahmedabad district. A population of 963 (446 urban & 517 rural) showed alarmingly adverse sex ratio (SR) as low as 562 among urban preschoolers. GD was prevalent in both study areas but manifested differently. Prefer...

Sex is determined in Drosophila by the activity of the Sex-lethal master regulator. Activity of Sex-lethal is initiated early in females by chromosome-counting transcription factors, then reinforced by signaling through the Janus kinase pathway.

The effect of linkage and epistasis on the evolution of the sex-ratio is studied in a symmetric two-locus model of autosomal sex determination closely related to the symmetric viability model of R. C. Lewontin and K. Kojima. R. A. Fisher's expectation of an even sex ratio for autosomal sex determination by a single gene governs the dynamics when the loci are tightly linked. However, recombinati...

Sex determination in honeybees involves a multi-allelic locus, such that homozygotes develop as males and heterozygotes as females. In this issue of Cell, report the cloning of the sex-determining gene, csd. It codes for an SR protein, and different alleles have very different amino-acid sequences. Inactivating csd leads to development as a male.

Sex in birds is chromosomally based, as in mammals, but the sex chromosomes are different and the mechanism of avian sex determination is a long-standing mystery. In the chicken and other birds, the homogametic sex is male (ZZ) and the heterogametic sex is female (ZW). Two hypotheses have been proposed for the mechanism of avian sex determination. The W (female) chromosome may carry a dominant-...

Sex in birds is chromosomally based, as in mammals, but the sex chromosomes are different and the mechanism of avian sex determination is a long-standing mystery. In the chicken and other birds, the homogametic sex is male (ZZ) and the heterogametic sex is female (ZW). Two hypotheses have been proposed for the mechanism of avian sex determination. The W (female) chromosome may carry a dominant-...

Sex in birds is chromosomally based, as in mammals, but the sex chromosomes are different and the mechanism of avian sex determination is a long-standing mystery. In the chicken and other birds, the homogametic sex is male (ZZ) and the heterogametic sex is female (ZW). Two hypotheses have been proposed for the mechanism of avian sex determination. The W (female) chromosome may carry a dominant-...

A century ago, Bridges proposed that male genes on the autosomes and female genes on the X chromosome compete to determine sexual identity. New genetic and molecular studies establish Caenorhabditis elegans as the first animal known to use this mechanism.