Margery W. Shaw

Individual pairs of human chromosomes can be reliably identified by a new method that does not require special optical equipment and that results in permanent preparations. This method, which is based on treatment of the chromosomes in situ with NaOH, followed by incubation in sodium chloride-trisodium citrate and Giemsa staining, results in highly specific banding patterns in characteristic regions of the chromosome arms. It should prove useful for the detection of small structural changes in chromosomes.

Genetic polymorphism has been demonstrated in man for many characteristics including blood groups, serum proteins, tissue enzymes, and hemoglobins. A class of chromosomal polymorphism involving constitutive heterochromatin has now been found. Through the use of a special technique that permits visualization of heterochromatin, seven heterochromatin variants have been found among four individuals. These results suggest a very high frequency of variability of heterochromatin in the population.

Variation in the length of the Y chromosome in a population of 100 males, derived from five different racial and ethnic sub-groups, was investigated. The Y chromosome and selected autosomes were measured in 1000 metaphase cells. Statistical analysis of the data demonstrates significant differences in mean length of the Y among some of the groups as well as among the individuals within each group. The mean length of the Japanese Y chromosome was significantly greater than that of all other groups. Among a sample of 736 circular metaphase plates, the Y chromosome was peripherally located in 241 cells.