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Taurine (Bos 'taurus') and zebu (Bos 'indicus') cattle were domesticated independently in the Near East and in India respectively (Beja-Pereira et al., 2006) and are believed to have diverged 117-275,000 years ago (Bradley et al., 2006). Bos 'taurus' cattle were introduced to Australia by European settlers in the end of the 18th century. The main 'B. indicus' breed used for beef production in Australia is the Brahman which was imported in the 20th century. The Brahman breed originated in the United States of America in the early 1900s where it was developed from progeny of four Indian cattle breeds with some infusion of British-bred cattle (http://www.brahman.com.au/history.html). Since then crossbreeding between Brahman and 'B. taurus' breeds has been used to form several composite breeds such as the Santa Gertrudis. Because this crossbreeding has been recent, large chromosome segments of either 'B. taurus' or 'B. indicus' origin should be segregating in these composite breeds. Due to their long separation and different selection pressures, 'B. indicus' and 'B. taurus' cattle may differ substantially in allele frequency at some genes affecting quantitative traits. If we can detect chromosome segments that derive from zebu or taurine origin, we can estimate their effect on quantitative traits and hence detect quantitative trait loci (QTLs) where there is a large difference in allele frequency between the sub-species. In this paper, we present two methods to determine the origin of a chromosome segment based on 50K SNP data and show that, at some positions in the genome, 'B. indicus' and 'B. taurus' chromosome segments differ in their effect on live weight or carcase weight. |
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