ABSTRACT
Periodicity in the distribution of prominent bands was analysed from the light and electron microscopic maps of salivary gland chromosomes of Drosophila melanogaster. The data obtained indicate that a similar distribution of prominent chromomeres in an individual interphase chromatid results in a unilateral accumulation of chromatin at the chromonema stage, if the helical axis of chromonema consists of ∼5-9 interchromomere + chromomere units per turn. Orientation of the largest chromomeres mainly on one lateral half and the smallest chromomeres mainly on the opposite lateral half of the chromonema apparently bends it to form the chromosomal ‘macro’ coil. Thus the increase in DNA content in the chromomeric loops located at specific intervals along the chromatids may have an important role in the evolution of coiling hierarchy in the eukaryotic chromosomes.
