Abstract

Although it is well known that variations in size are common in the centric heterochromatin of human chromosomes, it has not been appreciated that centric heterochromatin may be positioned either entirely on the short arm, centrally, or entirely on the long arm. Inspection of C banded karyotypes in which chromosomes were identified by previous Q banding showed C band position variants in all of the chromosomes of groups A, B, C, E, and F. These 'new' C band markers were followed in families and found to be heritable. By scoring chromosomes for both size and position of C bands it should be possible to distinguish the majority of homologous chromosomes in most people. The ease of scoring and high frequency of variation should make C band position variants extremely useful in linkage studies and population surveys.