Moderately repeated mouse Y chromosomal sequence families present distinct types of organization and evolutionary change.

Male specific repeated sequences compose approximately 10% of the mouse Y chromosome. This was deduced from studies of genomic phage clones that contain male specific DNA, and three subcloned EcoRI fragments pBC10-0.6, pBC15-1.1, and pBA33-1.8. Southern analyses and in situ hybridization of metaphase chromosomes show these three sequences to be present in 100-200 copies on the Y chromosome and in female DNA as single copies. One of these, pBC10-0.6, was directly demonstrated to be on the X chromosome. All three exhibited male specific transcription. These sequences are found in two distinct organizations. Subclone pBC10-0.6 is uniformly found in a long HpaI repeat unit of 9.7 Kbp. Subclones pBC15-1.1 and pBA33-1.8 are distributed throughout several EcoR1 repeat families in which the male specific fragments are interspersed. These male specific fragments also differ among themselves with regard to the types and frequency of evolutionary changes.