Comparative RH maps of the river buffalo and bovine Y chromosomes.

Radiation hybrid maps were constructed for river buffalo and cattle Y chromosomes. A total of 41 cattle-derived Y-chromosome molecular markers were selected and tested with 2 previously described 5,000-rad whole-genome radiation hybrid (RH) panels (river buffalo - BBURH(5000) and cattle - BTARH(5000)) for generation of maps. Among the initial 41 selected markers, a subset of 26 markers generated PCR products suitable for scoring with the BBURH(5000) panel. Of these, 19 markers (73%) were distributed in 1 linkage group spanning 341.3 cR. Retention frequencies (RF) for individual markers ranged from 17.8% for SMCY to 56.7% for BTY1, with an average RF of 37.6%. From the selected markers, 37 generated reliable scores using the BTARH(5000) panel. The newly constructed BTAY RH map contains 28 markers distributed within 1 linkage group. Twenty-four of these markers had been previously mapped on BTAY using a 7,000-rad cattle-hamster WG-RH panel and 4 markers were mapped for the first time (ZFY, SeqRep, RepSeqS4 and BTY1). The length of the BTAY RH map was estimated to be 602.4 cR. Retention frequencies for individual mapped markers ranged from 10% (INRA126) to 63.3% (SeqRep), with an average RF of 35.3%. RH marker positions along the Y chromosome were compared between BBUY and BTAY, which revealed differences in the order of some of the markers. The BBUY pseudoautosomal region (PAR) is delineated by 3 BTAY PAR markers (MAF45, TGLA325 and UMN2008). These markers are telomeric in both species but are not found in the same order. Here we have demonstrated the effective use of bovine Y chromosome markers for the development of the first BBUY RH map. Likewise, these set of markers can be used for comparative assessment of Y chromosomes in other members of the Bovidae family.