Extreme heterogeneity in sex chromosome differentiation and dosage compensation in livebearers

Darolti, I and Wright, A E and Sandkam, B A and Morris, J and Bloch, N I and Farré, M and Fuller, R C and Bourne, G R and Larkin, D M and Breden, F and Mank, J E (2019) Extreme heterogeneity in sex chromosome differentiation and dosage compensation in livebearers. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA.

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Abstract

Morphologically and functionally distinct X and Y chromosomes have repeatedly evolved across the tree of life. However, the extent of differentiation between the sex chromosomes varies substantially across species. As sex chromosomes diverge, the Y chromosome gene activity decays, leaving genes on the sex chromosomes reduced to a single functional copy in males. Mechanisms have evolved to compensate for this reduction in gene dosage. Here, we perform a comparative analysis of sex chromosome systems across poeciliid species and uncover extreme variation in the degree of sex chromosome differentiation and Y chromosome degeneration. Additionally, we find evidence for a case of chromosome-wide dosage compensation in fish. Our findings have important implications for sex chromosome evolution and regulation.