NanoString nCounter copy number variation assay

The sex chromosomes often follow unusual evolutionary trajectories. In particular, the sex-limited Y and W chromosomes frequently exhibit a small but unusual gene content in numerous species, where many genes have undergone massive gene amplification. The reasons for this remain elusive with a number of recent studies implicating meiotic drive, sperm competition, genetic drift and gene conversion in the expansion of gene families. However, our understanding is primarily based on Y chromosome studies, and the W chromosome has been largely overlooked. Here, we conduct a comprehensive investigation into the abundance, variability, and evolution of ampliconic genes on the W both across and within avian species. We find a striking deficit of gene families on the duck W chromosome, as well as conservation in W-linked gene copy number across duck breeds, indicating that gene amplification may not be such a general feature of sex chromosome evolution as Y studies would initially suggest. Furthe...