FISH, showing DAZ clusters in an unaffected man and in a man with a P5/proximal-P1 (AZFb) deletion. A, Representative interphase nucleus from a fertile, male control individual hybridized with cosmid 18E8 (yellow), showing two dots (corresponding to two DAZ clusters, each containing two DAZ genes). B, Representative interphase nucleus from P5/proximal-P1–deleted patient WHT4396, showing one dot (corresponding to one DAZ cluster). C, Histogram of number of nuclei observed grouped by number of dots per nucleus.