Results for interspecies competitive hybridization. The number of probes (y-axis) with a given nonhuman/human log₂ ratio (x-axis) is shown with black bars for the human probes and with clear bars for (A) chimpanzee probes (mean difference 0.50), (B) orangutan probes (mean difference 0.78), and (C) rhesus probes (mean difference 1.15). All three values are significantly higher than the experimental error estimated from the self-hybridization (P <10^–4), indicating that sequence differences affect hybridization intensity. Note that the normalization based on both species probe sets leads to a symmetric distribution (see Methods).