Zoological Studies

Vol. 47 No. 5, 2008

Fusions of Muller’s Elements during Chromosome Evolution of Drosophila albomicans

Te-Pin Chang1, Tai-Hua Tsai1, and Hwei-yu Chang1,2,*

1Department of Entomology, National Taiwan University, Taipei 106, Taiwan
2Biodiversity Research Center, Academia Sinica, Nankang, Taipei 115, Taiwan

Te-Pin Chang, Tai-Hua Tsai, and Hwei-yu Chang (2008) The karyotype of Drosophila albomicans differs from that of its sibling species D. nasuta by 2 fusions between a pair of autosomes and the sex chromosomes.  All species of the D. nasuta subgroup exhibit the fusion events involved in the basic karyotype of the D. immigrans species group, but 2 additional fusions evolved in D. albomicans.  This sibling species pair serves as a useful tool aided by the abundant DNA sequence information for D. melanogaster to correlate their chromosome arms to Muller’s elements.  Since the homologue of the 3rd autosome of D. nasuta is the long arm of the neo-sex chromosome of D. albomicans, genetic markers on it can be determined by checking sex-linkages from D. albomicans and D. nasuta hybrid crosses.  Three genetic markers were found to be located on this chromosome arm by crossing experiments and by female homozygotes and male heterozygotes in certain isofemale strains.  They were identified by BLAST as homologous to loci on the 2R and 3L chromosome arms of D. melanogaster, and therefore indicate correspondence of this arm to Muller’s elements C and D.  After a survey of sexual differences with several chosen sequences, 11 more loci were found which were also located on Muller’s elements C and D with no exceptions.  By in situ hybridization, the homologies were confirmed: 2L = B, 2R = E, and 3 = C + D.  Based on the hypothesized chromosome arm homologies between D. melanogaster and D. albomicans, the fusion events in lineages of Sophophora and Drosophila are discussed.

Key words: Drosophila nasuta, Homoplasy, Karyotype, Neo-sex chromosome.

*Correspondence: Te-Pin Chang and Tai-Hua Tsai contribute equally to this work.  E-mail:hwei@ntu.edu.tw