Length of Y chromosome and activity in boys.

In a cytogenetic-psychological study of 47 school boys in special classes and 48 controls in normal classes in a Danish city no significant difference was found between the mean Y length. There were, however, four boys with enlarged Y among the 47 in special classes, compared with one of the 48 in the normal classes. We found a significant correlation between length of Y and level of activity with increase of level of activity correlated with increase of length of Y when both groups were taken together (P is less than 0.005). The mean activity score was 6.5 for the boys with Y/F is less than or equal to 0.83, compared with 8.1 for those with Y/F greater than or equal to 0.95 (P is less than 0.005). If the milieu is restrictive with poor understanding and support for the needs of a boy, a comparatively large Y with associated high level of activity might intensify the problems of such a boy. If the milieu is positive, understanding, permissive and with possibilities of channeling activity, the large Y associated with a high level of activity might be a positive factor in personality and social adjustment. The present study shows certain tendencies confirming this.