The frequency of different types of satellite associations of nucleolar organizing human chromosomes (i.e. acrocentric chromosomes; 13, 14, 15, 21, and 22) is reported using 10 normal individuals by Ag-staining technique. The preferential involvement of acrocentric chromosomes in satellite association is suggested. Only acrocentric chromosomes with active NORs (i.e. Ag-stained) were found in association while unstained (inactive NORs) chromosomes were never seen in satellite association. In general as number of NORs expression increase, the frequency of association per cell was also increased. A possible mechanism and the clinical consequences of such an unusual phenophenon is described.

SUMMARYIn the present report we examined the position of the Y chromosome with respect to its size and race to determine their relationship to its peripheral location. Peripheral blood lymphocytes were cultured from 172 normal male individuals (70 Asian Indians; 49 American Blacks; and 53 Caucasians) and 2770 QFQ cells were photographed. The length of the Y chromosome was classified into four groups i.e., small, average, large and very large as described earlier (Verma etaL, J. Med. Genet., 15,227-281. 1978). The average incidence of peripheral location of all races for small, average, large and very large was 364, 5'84, 1051 and 11'17 per cent respectively. For blacks and caucasians, the peripheral location was influenced by its size while the incidence remained the same for Indians for all sizes. Consequently, it is presumed that the position of the Y chromosome in somatic metaphases depends upon race as well as its size.Furthermore, we have provided a method for determining the position of the Y chromosome which should suffice for most situations.

The human chromosomes of 'prophases' and 'prometaphases' reveal more bands that can be seen even in the best banded 'metaphase' chromosome. The