Variability in Length and Arm Ratio of the Pachytene Chromosomes of Corn

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Abstract
Chromosome length measurements are recorded for all chromosomes in the pachytene stage for 271 microsporocytes. The material came from 89 anthers of 31 related corn plants. Arm ratios were determined where it was possible to locate the centromere. The results suggest that longer chromosome arms have greater variances but smaller coefficients of variability than shorter arms. Also, chromosomes with larger arm ratios have inherently more variable arm ratios. Greater variability in arm ratios is not correlated with greater variability in length of the chromosomes involved. These findings are interpreted to mean that the chromosomes have two kinds of variability: (a) that which contributes uniformly per unit length throughout the genome, and (b) that variability which is characteristic of each chromosome, and unrelated to length. Chromosome knobs do not influence the variability in length of the chromosome arm on which they occur. Tripsacum chromosome material appears to react in a manner similar to maize.