Abstract
SUMMARYAn analysis of chromosome morphology and Feulgen cytophotometric measurements of the nuclear deoxyribonucleic acid (DNA) content for diploid, triploid, tetraploid, pen-taploid and hexaploid species of Betula was carried out. A direct correlation was found between the observed DNA absorbance and the chromosome number for the 28, 42, 56, and 70-chromosome plants. The DNA density value for the 84-chromosome plants was calculated to be approximately equivalent to that of a theoretical 61-chromosome plant. The average DNA value per unit length of chromosome was 0.283 units for the 84-chromosome plants in contrast to 0.350 units per unit length of chromosome for each of the other euploid levels. Total complement length for each level of ploidy increased with increasing chromosome number, although not in direct proportion. The observed reduction in nuclear DNA in the 84-chromosome plants did not appear to be directly related to any change in chromosome size.
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