Abstract: Petaloid toenails, a human trait where the nail of little toe appears petaloidly exists in many populations of the Han Nationality in North China. In order to examine the distribution of petaloid toenails in the population and to assess its hereditary mode, a household survey was carried out at a village located in Zhouzhi County, Shaanxi Province, China. It was found that, petaloid toenails consist of three types: clarity, amalgamation and degeneration. The frequency of petaloid toenails was 79. 17%, of which 81. 48% were found in men and 76. 67% in women. There was no statistical significance for gender ( x2= 1. 09, P = 0. 295) . Petaloid toenails appeared single-sided or double-sided, and again there was no statistical significance for gender( x2= 2. 94, P = 0. 23) . When subjects were classified into 13 groups by age, there was a statistical significance among the frequencies of petaloid toenails of the 13 age-groups ( x2= 28. 49, P= 0. 005) . Analyzing the data of 51 nuclear families and 2 families with 3 generations, it was found that petaloid toenail had the same hereditary characters as a dominant single-gene trait. Thus, it could be concluded that petaloid toenails is a dominant single-gene trait with various types, appearing singly
side or doubly-side; and its frequencies had no variance for gender, but variance for age.

Key words: Petaloid toenails; Types; Distribution; Hereditary mode; The Han Nationality