Accelerated pseudogenization on the neo-X chromosome in Drosophila miranda

Y chromosomes often degenerate via the accumulation of pseudogenes and transposable elements. By contrast, little is known about X-chromosome degeneration. Here we compare the pseudogenization process between genes on the neo-sex chromosomes in Drosophila miranda and their autosomal orthologues in closely related species. The pseudogenization rate on the neo-X is much lower than the rate on the neo-Y, but appears to be higher than the rate on the orthologous autosome in D. pseudoobscura. Genes under less functional constraint and/or genes with male-biased expression tend to become pseudogenes on the neo-X, indicating the accumulation of slightly deleterious mutations and the feminization of the neo-X. We also find a weak trend that the genes with female-benefit/male-detriment effects identified in D. melanogaster are pseudogenized on the neo-X, implying the masculinization of the neo-X. These observations suggest that both X and Y chromosomes can degenerate due to a complex suite of evolutionary forces.

Nozawa M, Onizuka K, Fujimi M, Ikeo K, Gojobori T (2016) Accelerated pseudogenization on the neo-X chromosome in Drosophila miranda. Nature Communications 7: 13659. Available:

We thank Chie Iwamoto and Miu Kubota for helping with our experiments and Masanori Toda for species identification. We are also grateful to Junichi Imoto, Yukako Katsura, Sonoko Kinjo, Norikazu Kitamura, Kaoru Matsumoto, Masatoshi Nei, Masa-aki Yoshida and Ikuko Yuyama for their comments on earlier versions of the manuscript. This work was supported by grants from the National Institute of Genetics and JSPS KAKENHI (Grant Numbers 25711023 and 15K14585) to M.N.

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