Model of the evolution of the AZFc amplicons on the primate Y chromosomes. The blue, the light-blue, and the distal portion of the yellow amplicons are the oldest amplicons and are present on the Y chromosomes of all primates. Duplication and transposition of autosomal sequences, depicted as arrows or blocks with the origin of the autosome indicated at right, to the human Y chromosome occurred in three waves as indicated with upward arrows. Today's yellow-amplicon in fact consists of three sections, represented in different colors, that arrived on the Y chromosome at different times. Additional amplifications of the red-amplicon occurred in the great ape lineage soon after the separation of the Old World monkey lineage. Subsequent duplications/deletions (not shown) in the various lineages generate a copy-number spectrum of red amplicon found in today's humans and great apes. See the text for details. The copy numbers of the gray-, green-, yellow- and blue-amplicons in the various primates have not been determined and only one each is shown. MYA: millions of years ago.