Discovery of a predicted gene arrangement in Drosophila azteca

A method which under certain conditions permits prediction of as yet undiscovered gene arrangements was described a few years ago.(1,2) Its essence is as follows. If an inversion transforms the gene arrangement ABCDEFGH into AEDCBFGH, a second inversion taking place in the altered chromosome may be of the overlapping type, that is one of the breaks of the second inversion may lie within and the second break outside the limits of the first inversion. Thus the arrangement AEDCBFGH becomes AEDGFBCH. If the first and the third of these arrangements are known, one can postulate the existence of AEDCBFGH as a necessary intermediate step. If a family of gene arrangements related as overlapping inversions is known, a phylogenetic scheme indicating the lines of descent within this family may be drawn. Occasionally such phylogenetic schemes involve hypothetical links constructed with the aid of the method just outlined. The purpose of the present note is to record an instance of the discovery of such an hypothetical link, and certain related facts.