On the evolution of sex determination

Area of Science:

• Immunogenetics
• Comparative Genomics
• Evolutionary Biology

Background:

• Female mice reject male skin grafts due to the H-Y transplantation antigen.
• Antibodies in females recognize a male-specific cell-surface antigen (serological H-Y).
• The distinction between transplantation H-Y (H-Yt) and serological H-Y antigens is under investigation.

Purpose of the Study:

• To examine the sex-specific expression of the serological H-Y antigen in a diverse range of vertebrate species.
• To investigate the correlation between H-Y antigen expression and different modes of sex determination.
• To explore the evolutionary origins of sex chromosomes and H-Y antigen expression.

Main Methods:

• Serological testing for H-Y antigen expression in 25 vertebrate species across seven major classes.
• Analysis of H-Y expression patterns in relation to known sex determination systems (e.g., chromosomal, temperature-dependent).
• Comparative analysis across diverse taxa, including fish, amphibians, reptiles, and birds.

Main Results:

• Sex-specific H-Y antigen expression was observed in all 25 studied species.
• A strong correlation was found between H-Y expression and the heterogametic-type gonad.
• Unusual H-Y expression patterns were noted in species with temperature-influenced sex determination and transitional systems.

Conclusions:

• The H-Y antigen is widely expressed in a sex-specific manner across diverse vertebrate groups.
• Heterogamety and sex-chromosome heteromorphism appear to be polyphyletic in origin.
• Common sex-determining genes may be conserved across different taxonomic groups despite independent evolution of sex chromosomes.