Evolution and survival on eutherian sex chromosomes

Area of Science:

• Evolutionary genetics
• Mammalian sex chromosome evolution

Background:

• Eutherian X and Y chromosomes evolved from an ancestral autosome.
• The Y chromosome has lost most genes, while the X remains gene-rich.
• The distinctiveness of retained Y-linked genes and the timing of sex chromosome divergence remain unclear.

Purpose of the Study:

• To investigate the evolutionary rates of X and Y homologous genes (gametologs) in eutherians.
• To compare the divergence of X-Y gametologs with autosomal orthologs in marsupials and monotremes.
• To understand the factors contributing to Y-linked gene retention.

Main Methods:

• Comparative genomics of X and Y gametologs across eutherian mammals.
• Analysis of autosomal orthologs in marsupial and monotreme mammals.
• Evaluation of experimental data on mRNA/protein expression and function.

Main Results:

• X and Y genes acquired distinct evolutionary rates immediately after recombination suppression.
• Y-linked genes evolved at higher rates; X-linked genes retained ancestral lower rates.
• Most human X and Y gametologs evolved under stronger purifying selection than autosomal paralogs.

Conclusions:

• Unique expression patterns and functions of Y gametologs likely drove their retention.
• Evolutionary divergence of sex chromosome strata may require redefinition.
• Distinct evolutionary trajectories of X and Y genes are maintained throughout mammalian evolution.