SEQUENCES OF GLOBIN-6 GENE ALLELES AND LINKAGE OF GLOBIN-6 AND GLOBIN-7B GENES IN THE INSECT CHIRONOMUS-THUMMI-THUMMI

The purpose of this study was to isolate the stage-specifically expressed Chironomus thummi thummi globin-encoding gene (Gb) 6 (ctt-6). The final product of this gene is hemoglobin (Hb) CTT-VI, a protein that is phylogenetically most closely related to Hb CTT-VIIB. In the absence of chromosomal rearrangement, genes of immediate common ancestry should be closely linked. This was shown for a genomic clone containing the Gb ctt-3 and ctt-4 genes (encoding Hb CTT-III and CTT-IV, respectively), and another clone containing the Gb ctt-2 beta and ctt-9a genes (encoding Hb CTT-II beta and CTT-IXa, respectively). We report the isolation and sequence of two alleles of Gb ctt-6 found on independent genomic clones screened with a ctt-6 cDNA, and the predicted linkage of Gb ctt-6 and a ctt-7B gene. The latter, designated Gb ctt-7B9/5, is unusual in being a chimera of two previously reported Gb ctt-7B genes. The result of a partial gene conversion or an unequal crossover between oppositely oriented genes, the chimeric ctt-7B9/5 represents either an additional ctt-7B locus or a 7B haplotype.