Figure 1. (A) Phylogeny of D. melanogaster (mel), its closest relatives (rel: D. simulans, D. sechellia, and D. mauritiana), and the outgroup species D. yakuba (yak). The Sperm dynein intermediate chain (Sdic) multigene family is only present in D. melanogaster and therefore it must have been originated after its lineage branched off from that leading to its closest relatives 5.4 mya.³⁶ (B) Details of the molecular organization of the Sdic multigene family at 19C1 of the X chromosome. Although four copies are annotated in FlyBase,²⁵ our computational analyses revealed the existence of additional haplotypes that denote the existence of further copies, in good agreement with earlier estimates (see main text). The presence of additional copies of the gene Sdic could conflict with models previously proposed for the generation of the multigene family.⁶