An interstitial deletion in mouse Y chromosomal DNA created a transcribed Zfy fusion gene.

The small portion of the mouse Y chromosome retained in the Sxra transposition is thought to carry at least five genes including, as demonstrated here, the entirety of the zinc-finger genes Zfy-1 and Zfy-2. Sxrb, a derivative of Sxra, was previously thought to retain Zfy-1 but to be deleted for Zfy-2. Here we show that Sxrb differs from Sxra as the result of unequal crossing-over between Zfy-1 and Zfy-2. This unequal crossing-over created a transcribed Zfy-2/1 fusion gene and an interstitial deletion. Our data and previous results together suggest that this deletion encompassed the 3' portion of Zfy-2, the histocompatibility gene Hya, the spermatogenesis factor Spy, and the 5' portion of Zfy-1. We suggest that not only Zfy but also other neighboring genes such as Spy and Hya may exist in two copies on the Y as the result of a large tandem duplication during rodent evolution.