Pachytene Chromosomes of Diploid Medicago sativa L.1

Abstract

Chromosomes at the pachytene meiotic stage of microsporocytes were measured and characterized in diploid Medicago sativa L. (2n = 16). An idiogram for the eight chromosomes of the haploid complement was constructed including the following details: average total lengths, arm lengths:, arm length ratios (long arm ÷ short arm lengths), and number, position, and size of chromatic areas. The chromosome lengths of the complement ranged from 25.4 to 40.1 microns, and arm length ratio ranged from 1.19 to 3.06. Large degrees of variability in length measurements from cell to cell were noted. Similarly, arm length ratios were also variable, but to a lesser degree. Because of the variability from cell to cell, absolute length was not reliable as an identification criterion. Relative lengths (within the cell), arm length ratios, and chromatic area patterns formed reliable criteria for identification of chromosomes when taken in combination.