Ahmed Hassan's first authored paper (Rob Ness Lab)
New Phytologist 2019
Across eukaryotes, sex-determining regions, such as the human X-Y chromosome system, tend to be crossover suppressed. While crossover suppression is useful in maintaining sex-specific genes on certain chromosomes, the lack of genetic exchange means that these regions often differentiate from one another and degenerate over time — think the human Y chromosome, for instance. However, the sex-determining regions of isogamous (i.e. with equal sized gametes) eukaryotes tell a different story: the sex-determining regions of unicellular eukaryote Chlamydomonas reinhardtii (also known as the MT locus) are somehow not very differentiated at all, despite being millions of years old and crossover suppressed themselves. However, recent work has shown that gene conversion, a form of unidirectional genetic exchange, can still take place within the C. reinhardtii MT locus. In this paper, we show that gene conversion is actually widespread across the MT locus, and that genes that undergo more of it are in fact more efficient at purging deleterious mutations. Thus, gene conversion allows these MT genes to not only remain in a more homomorphic state, but also avoid the degeneration typically seen in crossover-suppressed regions. Given that other examined isogamous species also show little evidence of differentiation in their sex-determining regions, our study suggests that this effect of gene conversion is widespread in other isogamous unicellular eukaryotes as well