Zoological Studies

Chromosomal Inversion Polymorphism in Natural Populations of Drosophila ruberrima

Shu Fang, Fei-Jann Lin and Hwei-yu Chang (1998) The standard map of the giant polytene chromosome of Drosophila ruberrima, one of the members of the immigrans species subgroup of the immigrans species group, is constructed according to the primitive gene arrangement or standard sequence (8T) for each chromosome. A pure line with homozygous chromosomes was established. Chromosomal inversions can be identified easily by crossing a male fly with the pure line and checking the F₁ with the aid of this standard map. Inversion polymorphism, both kinds and frequencies, of this species is high. The Taiwan population is at Hardy-Weinberg equilibrium, but the Yunnan population shows an excess of homozygotes which is probably affected by natural selection. The geographic pattern of chromosomal inversion polymorphism in natural populations reveals that the marginal island population, Taiwan, is less variable than the central mainland population, Yunnan, mainland China. Little genetic differentiation among subpopulations within Taiwan indicates that extensive gene flow exists. In contrast, moderate genetic differentiation was observed between the Taiwan and Yunnan populations.