DNA density in mitotic and meiotic metaphase chromosomes of plants and animals

Studies of chromosome disposition at metaphase using serial thin-sectioning and three-dimensional reconstruction techniques have produced accurate estimates of the total volume of chromosomes per cell in 15 plant and two animal species. Comparing this character with the 4C DNA amount showed no indiction of systemic differences in DNA density between either organisms with widely different (greater than 200-fold) C values or different groups or organisms. For example, there was no significant difference between the density of DNA in somatic metaphase chromosomes of man (0.141 pg/micrometers3) and its mean in 14 angiosperm plant species (0.182 pg/micrometers3), or between four dicotyledons (0.180 pg/miocrometers3) and 10 monocotyledons (0.182 pg/micrometers3). However, evidence was found showing that DNA density can vary significantly within a species. Thus, although the total chromosome volume per cell was closely correlated (r greater than 0.97) with 4C DNA amount in somatic and meiotic cells, the density of DNA in metaphase chromosomes was significantly lower in meiocytes (0.131 pg/micrometers3) than in somatic metaphase cells (0.19 pg/micrometers3).