Metaphase and chromomere banding are distinct entities of chromosome substructure

Haapala, O. 1984 Metaphase and chromomere banding are distinct entities of chromosome substructure. —Hereditas 100:75–81. Lund, Sweden. ISSN 0018–0661. Received May 27, 1983 Macrocoiled and banded appearances of human chromosomes were compared after specific hypotonicity in order to distinguish between chromosomes in respect of their mitotic stage of compaction, i.e. when chromatids are either macrocoiled (as in metaphase) or prior to macrocoiling (as in mid-metaphase and earlier stages), Altered hypotonicity (KC 1–NaNO3--CH3COONa) increased the proposition of uncoiled chromosomes about 10–fold but, in addition, some 20 per cent of chromosomes were banded. The “inborn” banding patterns of these chromosomes were identical, irrespective of whether chromosomes had separated or apposed chromatids. Measurement of chromosome length was used as an indication of the emergence of uncoiling and banding. Banded chromosomes were markedly less contracted than macrocoiled ones, as were those with apposed chromatids as compared to chromosomes with separated chromatids. The number of light-microscopic macrocoil gyri was decreasing towards shorter chromosome lengths, giving a false impression of gyre elimination as an in vivo mechanism of chromonemal compaction. It is suggested that banding in chromosomes prior to macrocoiling should be defined as chromomere banding. In view of chromatid substructures, chromomere banding is a distinct entity to metaphase banding of chromosomes with macrocoiled chromatids.