Detection of quantitative trait loci for growth and beef carcass fatness traits in a cross between Bos taurus (Angus) and Bos indicus (Brahman) cattle1

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Abstract
This study was conducted to detect quantitative trait loci (QTL) affecting growth and beef carcass fatness traits in an experimental population of Angus and Brahman crossbreds. The three-generation mapping population was generated with 602 progeny from 29 reciprocal backcross and three F2 full-sib families, and 417 genetic markers were used to produce a sex-averaged map of the 29 autosomes spanning 2,642.5 Kosambi cM. Alternative interval-mapping approaches were applied under line-cross (LC) and random infinite alleles (RA) models to detect QTL segregating between and within breeds. A total of 35 QTL (five with genomewide significant and 30 with suggestive evidence for linkage) were found on 19 chromosomes. One QTL affecting yearling weight was found with genomewide significant evidence for linkage in the interstitial region of bovine autosome (BTA) 1, and an additional 19 QTL were detected with suggestive evidence for linkage under the LC model. Many of these QTL had a dominant (complete or overdominant) mode of gene action, and only a few of the QTL were primarily additive, which reflects the fact that heterosis for growth is known to be appreciable in crosses among Brahman and British breeds. Four QTL affecting growth were detected with genomewide significant evidence for linkage under the RA model on BTA 2 and BTA 6 for birth weight, BTA 5 for yearling weight, and BTA 23 for hot carcass weight. An additional 11 QTL were detected with suggestive evidence for linkage under the RA model. None of the QTL (except for yearling weight on BTA 5) detected under the RA model were found by the LC analyses, suggesting the segregation of alternate alleles within one or both of the parental breeds. Our results reveal the utility of implementing both the LC and RA models to detect dominant QTL and also QTL with similar allele frequency distributions within parental breeds.