Paucity of Genes on the <i>Drosophila</i> X Chromosome Showing Male-Biased Expression

TLDR

Sex chromosomes are key determinants of sexual dimorphism, arise from ancestral autosomes, and are shaped by sex‑specific selection, making their comparison to autosomes well suited for genomic studies. The study aimed to assess global gene expression in *Drosophila melanogaster* to determine whether X‑chromosome genes are over‑ or under‑represented among those highly expressed in males. The analysis revealed a striking paucity of X‑chromosome genes with high male expression, and these genes are poorly conserved in *Anopheles gambiae*, indicating that the X chromosome is a disfavored location for male‑specific genes.

Abstract

Sex chromosomes are primary determinants of sexual dimorphism in many organisms. These chromosomes are thought to arise via the divergence of an ancestral autosome pair and are almost certainly influenced by differing selection in males and females. Exploring how sex chromosomes differ from autosomes is highly amenable to genomic analysis. We examined global gene expression in Drosophila melanogaster and report a dramatic underrepresentation of X-chromosome genes showing high relative expression in males. Using comparative genomics, we find that these same X-chromosome genes are exceptionally poorly conserved in the mosquito Anopheles gambiae. These data indicate that the X chromosome is a disfavored location for genes selectively expressed in males.