Chapter 23 Notes: Evolution of Genetic Systems: Figure WN23.10 - Degeneration of a newly formed Y chromosome in Drosophila miranda.

Figure WN23.10 - Degeneration of a newly formed Y chromosome in Drosophila miranda.

Figure WN23.10. Degeneration of a newly formed Y chromosome in Drosophila miranda. (A) The arrangement of seven genes in an approximately 40-kb region of the neo-X and neo-Y. Note that four transposable elements have fixed in the neo-Y. (B) Divergence in the lineages leading to the neo-X and to the neo-Y were inferred by using D. pseudoobscura as an outgroup. (Gray triangles) Amino acid substitutions; (green boxes) in-frame insertions/deletions; (blue boxes) frameshift mutations. Most genes show an excess of amino acid changes on the neo-Y, indicating degeneration. However, exu1 and cycB show faster amino acid divergence on the neo-X; other evidence shows that this is likely to be due to positive selection. (C) Levels of Tajima’s D statistic and nucleotide diversity, π, across five regions of the neo-Y (see A). Negative Tajima’s D indicates an excess of rare variants; this, together with reduced diversity, is consistent with positive selection at exu1. Asterisk indicates significant deviations from neutrality at the 5% level (Bachtrog 2003). (Redrawn from Figs. 1a, 2, and 1b of Bachtrog 2003.)

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