Karyotypes of the D. melanogaster and obscura species groups. In the obscura group, which includes D. pseudoobscura and D. miranda, a translocation of Muller’s element D (white) to the X chromosome (gray) results in a karyotype where autosomal loci in the melanogaster group are X-linked in the obscura group. This new X chromosome was created ∼13 Mya. In this figure, the neo-sex chromosomes in D. miranda (which result from rearrangements between the Y chromosome and an autosome) are not shown for simplicity.