47,XXY males: sex chromosomes and tooth size

Permanent tooth crowns of 47,XXY males were found to be generally larger than those of control males and females and their first-degree male and female relatives. These results suggest that tooth-size increase in 47,XXY males is due to a direct genetic effect and support the concept of the presence of a specific growth gene (or genes) in the human X and Y chromosomes. The effect of this gene (or genes) seems to be the promotion of tooth growth, and the Y chromosome is more effective than the X chromosome in this respect.