Selective protection of specific DNA sequences in the heterochromatin of C-banded human Y chromosomes.

The molecular basis of C-banding was investigated by in situ hybridization of human Y chromosome-derived repeated sequences, DYZ1 and DYZ2, to untreated or to alkaline-treated metaphases. Autoradiography of G-banded metaphases showed that both probes hybridized to the long arm of Y. Alkaline hydrolysis significantly reduced grain number for DYZ2 (58%-82%; P less than .05) but not for DYZ1 (P greater than .05). Similar results were observed for interphase nuclei. These findings demonstrated that the heterochromatin of the long arm contains at least two repetitive DNA fractions having two different sensitivities to alkaline hydrolysis. These observations support the notion that DYZ2 maps terminally on the Yq arm and may be nonheterochromatic.