The data of 21 families were analyzed by the method of Slater's calculating model to differentiate between single-gene and multi-gene heredity and by the method of non-deviation analysis. The results showed that the hereditary mode of handedness or preferential foot or hand-clasping is the dominant heredity of single gene of autosome, and the right type of all of them is the dominant character. In a way, although environmental factors affected the phenotypes of these characters,hereditary factors were also the decisive ones.