Supplementary Note 3
In addition to its centromeric heterochromatin (approximately 1 Mb, ref. 1), the Y chromosome was previously shown to contain a second, much longer heterochromatic block (roughly 40 Mb) that comprises the bulk of the distal long arm (Fig. 1)2-4.
1. Tyler-Smith, C. et al. Localization of DNA sequences required for human centromere function through an analysis of rearranged Y chromosomes. Nat. Genet. 5, 368-675 (1993).
2. Caspersson, T., Zech, L., Johansson, C. & Modest, E. J. Identification of human chromosomes by DNA-binding fluorescent agents. Chromosoma 30, 215-227 (1970).
3. Pearson, P. L., Bobrow, M. & Vosa, C. G. Technique for identifying Y chromosomes in human interphase nuclei. Nature 226, 78-80 (1970).
4. George, K. P. Cytochemical differentiation along human chromosomes. Nature 226, 80-81 (1970).