The objectives of this project are: 1. To determine the degree of variability and heritability of the structure of the human iris. 2. To investigate through cross-sectional twin studies the possible structural and pigment differences in the iris of individuals in different age groups. 3. To develop, through dermatoglyphics and iris structure, further criteria for twin zygocity diagnosis. 4. To determine the genetic vs. intrauterine effect on the formation of dermatoglyphics and their association with disease. Thorough eye examinations, color slides of the irises and finger and palm prints, data were obtained from over 600 pairs of twins varying from new born to the age of seventy years old. Zygocity was established by elaborate blood group typing, perinatal information, and physical similarities. In addition to the twins we are also including in this study 250 pairs of sibs to serve as controls.