Structure of repeated sequences in the centromeric region of the human Y chromosome.

Alphoid satellite DNA is a family of sequences with an approximately 170 bp periodicity which is found near the centromere of all human chromosomes. The structure of the human Y-chromosome alphoid DNA has been studied in two somatic cell hybrids, 3E7 and 853 (Tyler-Smith & Brown, 1987). The 170 bp alphoid subunits are tandemly repeated and are organized into units approximately 5.7 kb long. A few variant units on the 3E7 Y chromosome contain two extra 170 bp subunits and are approximately 6.0 kb long; the variant units are present in two clusters at least 90 kb apart on the chromosome. On each Y chromosome there is a single major block of alphoid DNA: on the 3E7 Y chromosome it is approximately 440 kb long and on the 853 Y chromosome it is approximately 540 kb long. A long-range restriction map of the 853 block has been constructed covering approximately 1.1 mb of DNA. The distribution of restriction sites suggests that the sequences on one side of the alphoid block may be typical euchromatic DNA, while the sequences on the other side may be another satellite sequence.