CANDIDATE GENE ANALYSIS OF GH1 FOR EFFECTS ON GROWTH AND CARCASS COMPOSITION OF CATTLE

We present an approach to evaluate the support for candidate genes as quantitative trait loci (QTLs) within the context of genome-wide map-b ased cloning strategies. To establish candidacy, a bacterial artificia l chromosome (BAC) clone containing a putative candidate gene is physi cally assigned to an anchored linkage map to localise the gene relativ e to an identified QTL effect. Microsatellite loci derived from BAC cl ones containing an established candidate gene are integrated into the linkage map facilitating the evaluation by interval analysis of the st atistical support for QTL identity. Permutation analysis is employed t o determine experiment-wise statistical support. The approach is illus trated for the growth hormone 1 (GH1) gene and growth and carcass phen otypes in cattle. Polymerase chain reaction (PCR) primers which amplif y a 441 bp fragment of GH1 were used to systematically screen a bovine BAC library comprising 60 000 clones and with a 95% probability of co ntaining a single copy sequence. The presence of GH1 in BAC110R2C3 was confirmed by sequence analysis of the PCR product from this clone and by the physical assignment of BAC110R2C3 to bovine chromosome 19 (BTA 19) band 22 by fluorescence in situ hybridisation (FISH). Microsatelli te KHGH1 was isolated from BAC110R2C3 and scored in 529 reciprocal bac kcross and F-2 fullsib progeny from 41 resource families derived from Angus (Bos taurus) and Brahman (Bos indicus). The microsatellite KHGH1 was incorporated into a framework genetic map of BTA19 comprising 12 microsatellite loci, the erythrocyte antigen T and a GH1-TaqI restrict ion fragment length polymorphism (RFLP). Interval analysis localised e ffects of taurus vs, indicus alleles on subcutaneous fat and the perce ntage of ether extractable fat from the longissimus dorsi muscle to th e region of BTA19 harbouring GH1.