Telomeric heterochromatin (tHC)

At the ends of almost all polytene chromosomes appeared dot-like compaction of chromatin, which in phase contrast appeared black or in the DAPI fluorescence very bright (see figure a). In their presence and their expressions the dot-like compaction correspond to those structures described by that Schweizer (1976b) as telomeric heterochromatin.

The individual dots of the telomeric heterochromatin (tHC) were depending on the state of condensation of the surrounding chromatin (figure b). If the chromatin was loose, then the single dots of the tHC were individually identifiable (arrows). Appeared the chromatin in the vicinity of tHC, however, condensed, then the dots of tHC formed a highly packed accumulation. These accumulations could take various forms, such as a band like in Figure b (arrowhead).

Figure: Telomeric heterochromatin (tHC) of the polytene chromosomes of Phaseolus coccineus cv. Preisgewinner. (a) dot-like structures of the tHC (arrows) at the end of chromosome A in phase contrast (left) and of another chromosome A in DAPI fluorescence (right). At the chromosome in phase contrast (left) the tHC seems to lie on top of the collecting nulcoelus (ger. Sammelnukleolus)(SNuk). (b) Depending on the degree of condensation of the surrounding chromatin the dot-like structures were either individually identifiable (arrows) or densely packed (arrowhead, top left).
Scale bar represents 10 µm.