Polymorphism of the human Y chromosome: Fluorescence microscopic studies on the sites of morphologic variation

Normalized measurements were derived from quinacrine mustard stained normal‐ and variant‐size (large and small) human Y chromosomes. These measurements were used to study three problems: (1) the mechanism underlying the evolution of common heritable variations in the length of the long arm (q) ‐ All variants demonstrated differences in length of the distal fluorocenter, and some differed from normal by an integral length (e. g., the fluorocenter of subject Large Y was twice the normal size), Y's from one subject (Short Y‐e) were also shortened in the weakly fluorescent, proximal portion, the length of which was about one fourth the normal length. These data suggest that duplications or deletions of finite lengths (possibly a basic subunit) of chromosome are one means by which the variants have evolved. (2) the extent of Yq that is genetically dispensible, and presumably inactive ‐ Variations in the Y fluorocenter produce no phenotypic effect. Additionally, Y's from a previously reported kindred have a 50 % deletion, and those from subject short 4‐e about a 75 % deletion of the weakly fluorescent portion of Yq. Although Short Y‐e demonstrates the features of dyschondrosteosis, it seems that both the fluorocenter and 50–75 % of the weakly fluorescent portion of Yq are genetically inactive. (3) the position of the secondary constriction in Yq ‐ The position of the secondary constriction is virtually identical with the origin of the fluorocenter.