DISTRIBUTION OF POLYMORPHIC GENE DUPLICATION AT THE GPDH LOCUS IN NATURAL-POPULATIONS OF DROSOPHILA-MELANOGASTER

The glycerol-3-phosphate dehydrogenase (GPDH, E.C. 1.1.1.8) gene of Dr osophila melanogaster contains a tandem duplication of a 4.5-kb-long D NA fragment. Survey of the Gpdh gene region by the Southern blot analy sis revealed the following features of this gene duplication: (1) The duplication was not observed in chromosome lines that carry In(2L)t, a cosmopolitan chromosomal inversion in this species. The duplication a nd the inversion are in linkage disequilibrium. (2) The duplication is polymorphic in the Japan and US natural populations examined. Its fre quency is 0.26 on an average in In(2L)t-free chromosomes. (3) Triplica tion is absent or has not become frequent in the populations surveyed. Possible evolutionary factors of this duplication polymorphism are di scussed.