Molecular Mapping and Marker-Assisted Breeding for Muscle Growth and Meat Quality
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2009 by Taylor & Francis Group, LLC. Cattle coat color traits were selected for by the Romans, and ancient Egyptians were known to have polled cattle (Castle 1920). Selection for meat quantity and quality has probably occurred to varying degrees in domesticated meat animal species during the past 10,000 years, although identification of animals to be selected was a more difficult task than a simple choice of coat color. The effects on meat quality after selection of double-muscled animals to increase hindquarter size was discussed in the literature as early as the beginning of the nineteenth century ((Cully 1807; Youatt 1834) as reviewed in (Oliver and Cartwright 1969)). Bradford (1967) suggested that selection methods would be driven more by the availability of measurement techniques than by the size of the heritability coefficient, and that prediction seems to have held true. Cover et al. (1956) tested the belief that the tenderness and juiciness of steaks from yearling steers resulted from the fatness of the animal. In this particular study, estimated carcass fat was not associated with tenderness, although ether extract of fat from the ribeye was correlated. The authors determined, however, that fatness alone was not responsible for all of the variability observed in tenderness and juiciness. A subsequent investigation (Cover et al. 1957) demonstrated the influence of heredity on tenderness, but the authors noted that the evaluation of breeding animals is a problem since no suitable, quick method of live animal evaluation for tenderness is now available. Now, more than half a century later, a relatively small but still growing number of DNA marker tests can be utilized for selection of breeding stock for traits including meat quality. The molecular tools and gene maps that can be used for marker-assisted selection and breeding strategies to improve meat production have only developed over the past 25 years, especially during the past decade (reviewed in Womack 2005). In cattle, for example, initial efforts began with construction of synteny maps to identify groups of genes located on the same chromosome (e.g., Womack and Moll 1986). These early maps were later combined with physical maps generated by in situ hybridization (ISH) or other techniques (e.g., Fries et al. 1986; Gaye et al. 1986), and linkage maps that were constructed as polymorphic markers and hybridization probes became available (e.g., Hallerman et al. 1987).
