Gene-rich X chromosomes implicate intragenomic conflict in the evolution of bizarre genetic systems

Abstract

Significance Sex determination systems such as haplodiploidy, in which males' gene transmission is haploid, are surprisingly common, however, the evolutionary paths to these systems are poorly understood. X chromosomes may play a particularly important role, either by increasing survival of males with only maternal genomes, or due to conflicts between X-chromosomal and autosomal genes. We studied X-chromosome gene richness in three arthropod lineages in which males are diploid as adults but only transmit their maternally inherited haploid genome. We find that species with such atypical systems have far more X-chromosomal genes than related diploid species. These results suggest that conflict between genetic elements within the genome drives the evolution of unusual sex determination systems.