A twin study of the structure of human hair medulla

The genetic basis of hair medulla was studied by the twin method. Hair samples from 17 pairs of monozygotic (9 female and 8 male), 23 pairs of like-sex dizygotic (6 female and 17 male) and 8 pairs of unlike-sex dizygotic twins were utilized and the number of hair strands examined was 9,600. The mean intrapair differences indicate the presence of a strong genetic basis of the character concerned.