Frequencies of Heteromorphisms

Abstract

An initial attempt to assess the frequency of variants was made in non-banded chromosomes from consecutive newborns by Lubs and Ruddle (Science 169:495–497, 1970). Their study included 3,476 infants of white mothers and 807 infants of black mothers, all of whom were phenotypically normal except one child with low birth weight. A total of 2,131 variants involving chromosomes A1, C9, E16, the short arms and satellites of D and G group chromosomes, and Y long arm were scored. Frequencies of certain striking variants were found to be discrepant between black and white children (Table 3.1). In particular, a metacentric C9 variant (later recognized as a 9qh inversion) was 20 times more frequent in the black children; a large short arm on a D-group chromosome was four times more frequent. Y chromosome length was not different for black and white children. However, a large Y (> E18) was present in one of nine Chinese infants included in the study and a second large Y was present in the only Turkish infant. Earlier studies had shown a high frequency of large Y in Japanese adult males (Lubs and Ruddle, Nature 233:134–136, 1971).