Figure 1.

The structure of the human Y chromosome (features are shown approximately to scale). The black regions at each end of the Y chromosome are the pseudoautosomal regions, which cross over with homologous sequences on the X chromosome. The gray regions are heterochromatin. The white region contains the 23 megabase portion of the Y chromosome sequenced by Skaletsky et al. [7] (modified from Figure 1 of [7]).