Heritable fragile sites on human chromosomes. IX. Population cytogenetics and segregation analysis of the BrdU-requiring fragile site at 10q25.

The frequencies of the bromodeoxyuridine (BrdU)-requiring fragile site at 10q25 in 1,026 unselected neonates, 901 patients referred for chromosome studies, and 87 institutionalized retardates were not significantly different from each other. The gene frequency was .013, and the population was in Hardy-Weinberg equilibrium. Segregation analysis confirmed that the fragile site followed codominant inheritance. This fragile site and its nonfragile allelomorph can be considered to constitute the first true chromosomal polymorphism to be described in man.