Distribution of constitutive heterochromatin which is discernible by knobs, C- and Q-bands in maize was studied in the races of maize from the Americas and maize collections from the Northeastern Himalayas. Maize, being a highly cross-pollinated crop, shows a lot of heterozygosity in the population, and the differences are observable within different kernels of the same ear. Therefore, different plants of the same population also show variation in knob and/or band number.

Tables 1 and 2 show the close correspondence between knobs and C- and Q-bands. M-15, M-25, S-31 and M-14 exhibit an exact correspondence in both number and position of knobs and C-bands. M-1 shows a 1:2 correspondence between knob number and C-bands. The observation can be explained by the fact that, if homologous chromosomes are homozygous for the knob forming region, then double the number of bands will be observed in somatic metaphase, as compared to the pachytene knobs, where the homologous chromosomes are paired together. S-35 and S-20 also show a 1:2 correspondence between knobs and C-bands, but when the positions are compared, knobs which are subterminal in position were manifested as terminal C-bands because of the greater condensation of the somatic metaphase chromosomes.

T-2 and S-35 have shown an exact 1:1 correspondence between number and position of C- and Q-bands. M-1 shows 1:1 correspondence between number of C- and Q-bands, but subterminal C-bands are observed as terminal Q-bands, as the tails are sometimes very difficult to discern. But in general, distribution and pattern of Q-bands correspond to those of C-bands.

Table 1. Comparison between knob and C-band distribution

Table 2. Comparison between C- and Q-band distribution

Suchira Pande, J. K. S. Sachan and K. R. Sarkar

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