The Amylase gene cluster on the evolving sex chromosomes of Drosophila miranda

On the basis of chromosomal homology, the Amylase gene cluster in Drosophil a miranda must be located on the secondary sex chromosome pair, neo-X (X2) and neo-Y, but is autosomally inherited in all other Drosophila species. Ge netic evidence indicates no active amylase on the neo-Y chromosome and the X2-chromosomal locus already shows dosage compensation. Several lines of ev idence strongly suggest that the Amy gene cluster has been lost already fro m the evolving neo-Y chromosome. This finding shows that a relatively new n eo-Y chromosome can start to lose genes and hence gradually lose homology w ith the neo-X. The X2-chromosomal Amy1 is intact and Amy2 contains a comple te coding sequence, but has a deletion in the 3'-flanking region. Amy3 is s tructurally eroded and hampered by missing regulatory motifs. Functional an alysis of the X2-chromosomal Amy1 and Amy2 regions from D. miranda in trans genic D. melanogaster flies reveals ectopic AMY1 expression. AMY1 shows the same electrophoretic mobility as the single amylase band in D. miranda, wh ile ectopic AMY2 expression is characterized by a different mobility. There fore, only the Amy1 gene of the resident Amy cluster remains functional and hence Amy1 is the dosage compensated gene.