Selection for breed-specific growth hormone and IGF-I alleles in a synthetic beef cattle cross, Canchim

L.C.A. Regitano J.L. Azevedo R. Vencovsky I.U. Packer P.F. Barbosa A.J.M. Rosa N.A. Silva M.A.L. Etchegaray L.L. Coutinho About the authors

This study was developed to evaluate selection effects on gene frequencies in a synthetic beef cattle cross (5/8 Charolais, 3/8 Zebu) named Canchim. A sample of 154 Canchim animals, representing three generation classes, was analyzed for seven molecular markers. Thirty-six Charolais cattle were also studied for comparison. A highly significant variation (P < 0.01), with a linear increase of the allele coding for valine at position 127 of the growth hormone peptide, was observed through generations. This allele was found in the Charolais sample but is not observed in Brazilian Bos indicus breeds. Four alleles were found for a microsatellite in the 5' flanking region of insulin-like growth factor I gene in Canchim. Allele sizes ranged from 231 to 225 bp. There was a significant (P < 0.05) nonlinear increase in the 225-bp allele frequency. This allele was not observed in Charolais. Six alleles were observed for microsatellite CSFM50 in the Canchim population. A significant (P < 0.05) linear reduction of the 168-bp allele was observed over the generations. The hypothesis of preferential mating for growth hormone polymorphism was supported by Wright's F-statistics. Estimated FIS value for growth hormone was 0.59 (P < 0.01). These results suggest that selection influenced three out of seven loci analyzed. The simultaneous increases of a Bos taurus-specific growth hormone allele and a Bos indicus-specific insulin-like growth factor I allele indicate that phenotypic selection favored different regions of both genomes.

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