Normal Population Studies

Abstract

The first major population studies of human chromosomes were an eventual collaborative effort with data collected from 56 952 newborns from six different countries [1–7]. These, for the larger part, were initiated on unbanded chromosome material and in most centers were based on examination of two to five metaphases from each subject. The frequency of major chromosome abnormalities from these studies forms the basis of much of the statistical knowledge relating to frequencies of the major chromosome abnormalities, both numerical and structural. In tabulations of the results of these studies [8], however, there was a conscious effort to exclude normal morphological variants. The rationale for this was that, even though variants of certain chromosomes were well known, chromosome banding techniques were discovered before most of these studies were completed, so that it was quickly realized that accurate determination of variants in the majority of chromosomes was not possible in non-banded material. Nevertheless, a specific attempt to assess variants in unbanded chromosomes from 4482 consecutive newborns was made by Lubs and Ruddle [9] in New Haven, Connecticut. Their study included 3476 infants of White mothers and 807 infants of Black mothers. All of the children were phenotypically normal except for one White child with low birth weight. Criteria for the most common variants were established for chromosomes A1, C9, E16, the short arms and satellites of D and G group chromosomes, and Y long arm. A total of 2131 variants were scored.