Plant & Animal Genome IX Conference Plant & Animal Genome IX Conference
Workshop: Cattle/Sheep
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The ovine Carwell locus, originally identified in Australian Poll Dorsets, confers a mean 7% increase in longissimus dorsi (rib-eye) muscle weight, without any apparent effects on other muscle groups. Interestingly, Carwell has been mapped to the telomeric end of sheep chromosome 18, placing it in the same region as Callipyge, another locus for extreme muscling in sheep. In contrast to Carwell, inheritance of Callipyge results in generalised muscular hypertrophy, particularly pronounced in the hindquarters. It is possible that Carwell and Callipyge represent different mutations of the same gene although there is conflicting evidence for this. Both Callipyge and Carwell influence muscle development and localise to the same chromosomal region. However, Carwell displays a simple autosomal dominant pattern of inheritance whereas the Callipyge mutation exhibits an unusual mode of inheritance, known as polar overdominance. Only heterozygous animals which inherit the Callipyge mutation from their fathers exhibit muscular hypertrophy. Analysis of gene/EST maps and draft DNA sequence for the homologous region of the human genome (HSA14q32), using a variety of publicly available databases, has resulted in the identification of several positional candidate genes. A number of strategies, including further fine-mapping of genes in the region, are now being pursued in an effort to identify the gene mutation responsible for the Carwell phenotype and to determine whether Carwell and Callipyge are indeed different mutations of the same gene.