Copy number variation of testis-specific protein Y-encoded (TSPY) among different breeds of cattle (Bos taurus) and related individuals

Multi-copied gene families are prevalent in mammalian genomes especially within the Y chromosome. Gene copy number variation can impact phenotype and is becoming more appreciated as a source of global variation. Testis specific protein Y-encoded (TSPY) is present in variable copy number in many mammalian species. Cattle, for example, have copies numbers ranging from 50-200. The purpose of this study was to investigate the extent to which TSPY copy number varies among bulls, between different breeds of cattle and between related (step-brother) bulls. To investigate TSPY copy number we used relative real time polymerase chain reaction (PCR) to analyze the DNA of fourteen different cattle breeds and four sons of a single sire. The results showed variation both between and within breeds. Brown Swiss (161 copies, CI = 133-195) had significantly higher levels of TSPY and Western Fjord (65 copies, CI = 45-86) had significantly lower levels than some breeds, although most breeds had similar average TSPY copy numbers. All bulls showed within-breed variation. The TSPY copy numbers of the sons ranged from 55-75 copies and were found to differ significantly. These results show that copy number variation of TSPY can be seen within a single generation. This study demonstrates that copy number variation of TSPY is extensive in the bovine population; however, the purpose of this variation still remains a mystery.