Polymorphism on Chr Y was detected by polymerase chain reaction (PCR) for zinc finger protein 2, Y linked (Zfy2) with primer pairs (forward primer 50-GTGAGAGG CACAAGTTGGC-30 and reverse primer 50-GTGCTCCTG GTATGGTGTAT-30) for distinguishing Chr Y between Mus musculus musculus and Mus musculus domesticus (Prager et al. 1997).