Memoirs: Transverse Segmentation and Internal Differentiation of Chromosomes

Abstract

(1) The tendency for chromosomes to become transversely segmented or constricted is a wide-spread characteristic. It becomes operative especially, but not solely, whenever the chromosomes are short in comparison with their length, as happens normally in meiosis, and exceptionally in somatic tissues. (2) The point at which the constriction or segmentation takes place in any given chromosome is constant for that chromosome, and is the same as the point at which it most readily bends to form the angle of the V when present in that form. (3) The constancy of the position at which transverse segmentation takes place indicates a constant differentiation of the chromosomes in a lengthwise direction. (4) The presence of transverse constrictions or joints in chromosomes is not, without special evidence, to be taken as an indication of bivalency, or of a future division plane.