C banding in polytene chromosomes of Simulium ornatipes and S. melatum (Diptera: Simuliidae).
Polytene and mitotic chromosomes of Simulium ornatipes and S. melatum were subjected to C banding procedures. In both species polytene chromosomes consistently show C banding of centromere regions, telomeres, nucleolar organiser and, unexpectedly, numerous interstitial sites. The interstitial C banding sites correspond to morphologically single polytene bands. Their response is graded and independent of band size. Interstitial C bands in S. ornatipes are scattered throughout the complement, whereas in S. melatum they are clustered. Supernumerary heterochromatic segments in S. ornatipes also exhibit strong C banding and inverted segments can differ from standard in C banding pattern. -- Mitotic chromosomes of both species show a single centric C band with indications of two weak interstitial bands in S. ornatipes, suggesting that many C band regions, detectable in polytene chromosomes, are not resolved by present techniques in mitotic chromosomes. -- Contrary to current opinion that C banding is diagnostic for constitutive heterochromatin, the interstitial C band sites of polytene chromosomes are regarded as euchromatic. Conversely, the heterochromatic pericentric regions of S. ornatipes are not C banded. -- It appears that polytene chromosomes offer a promising system for the elucidation of C banding mechanisms.
D000818:Animals; D002843:Chromatin / Q000032:analysis; D002875:Chromosomes / Q000032:analysis*; D004175:Diptera / Q000166:cytology*; D006570:Heterochromatin / Q000032:analysis; D007739:L Cells / Q000166:cytology; D008938:Mitosis; D013045:Species Specificity; D013194:Staining and Labeling
D002843:Chromatin; D006570:Heterochromatin