THE EVOLUTIONARY HISTORY OF THE AMYLASE MULTIGENE FAMILY IN DROSOPHILA-PSEUDOOBSCURA

In Drosophila pseudoobscura, the amylase (Amy) multigene family is con tained within a series of inversions, or gene arrangements, on the thi rd chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL) inversions are central to the phylogeny of arrangements, and have clus ters of other arrangements derived from them. The gene arrangements be longing to each of these three clusters have a characteristic number o f Amy genes, ranging from three in ST to two in SC to one in TL. This distribution pattern can reflect a history of either duplications or d eletions, although the data available in the past did not permit a dec ision between these alternatives. We provide unambiguous evidence that three Amy genes were present before the divergence of the ST, SC, and TL arrangements. Thus, the current status of the Amy multigene family is the result of deletions in the TL and SC arrangements, which creat ed three new pseudogenes: TL Amy2-psi, TL Amy3-psi, and SC Amy3-psi. A nalysis of pseudogene sequences revealed that, in the SC and ST arrang ements, pseudogene evolution has been retarded, most likely due to the homogenization effect of gene conversion. Finally, by determining the original copy number, we have reconstructed the evolutionary history of the Amy multigene family and linked it with the evolution of the ce ntral gene arrangements.