Marcadores moleculares e seus efeitos sobre características quantitativas de bovinos de corte

Abstract

The most recent technologies of molecular biology have made it possible to access genetic variability at the molecular level, enabling the study of the connection between polymorphisms at the level of DNA with characteristics of economic importance in beef and dairy cattle. Three molecular markers, K-casein (CSN3), p-lactoglobulin (LGB) and growth hormone (GH) were used in order to study the effects of these markers on growth and fattening of beef cattle. A total of 633 animals, 325 cows, daughters of 14 bulls and 308 calves, sons of 8 bulls, were genotyped for each marker by means of PCR-RFLP, the genotypes being registered for further linkage study with quantitative characteristics. After optimizing the amplification reactions for each marker, the following parameters were obtained: CSN3 - 50 ng of DNA, 1 mM of MgCI2, 5 pmoles of dNTPs, 3 pmoles of each primer and 0.75 U of Taq DNA polymerase , under 94 ° C of initial denaturation for 5 ', followed by 35 cycles' at 94 ° C - 20 ”, 60 ° C - 30” and 72 ° C - 40 ”, plus 5' of final extension; LGB - 50 ng of DNA, 1 mM of MgCl2, 8 nmoles of dNTPs, 3 pmoles of each primer, 0.75 U of Taq DNA polymerase, under 94 ° C -5 ', 5 cycles 95 ° C - 20 ” , 60 ° C - 10 ”and 75 ° C - 40”, 10 cycles 95 ° C - 20 ”, 60 ° C - 10” minus 0.5 ° C / cycle and 75 ° C - 40 ”plus 20 cycles 95 ° C 10 ”, 55 ° C - 10”, adding TV cycle, 75 ° C - 40 ”, adding TV cycle and final extension 75 ° - 5 '; GH - 50 ng of DNA, 1 mM of MgCl2, 8 nmoles of dNTPs, 8 pmoles of each primer and 0.75 U of Taq DNA polymerase, under 35 cycles at 94 ° C, 62 ° C and 72 ° C - T each. The average gene frequencies observed in the calves were 0.85 and 0.15 for CSN3 alleles A and B, respectively; 0.30 and 0.70 for LGB alleles A and B, respectively; 0.37 and 0.63 for GH allele C and D, respectively. In cows the frequencies found were 0.84 and 0.16, respectively, for CSN3 alleles A and B; 0.29 and 0.71 for alleles A and BV of LGB, respectively and 0.32 and 0.68, for alleles C and D of GH. In the Nellore calves there was a Hardy-Weinberg balance deviation, which was attributed to genetic drift. The association of the genotypes of each marker with the quantitative characteristics was tested by three statistical models, the first (model I - univariate analysis of variance) and the second (model II - allelic substitution - linear regression) disregarding the effect of bulls, while that in the third, a comparison between genotypes grouped within families was used (model III). In models I and II the effects of bull and genotype were confused, showing associations between genotypes and significant quantitative characteristics. However, the analysis of data by family (model III) resulted in the absence of association, showing that in the families analyzed, the polymorphism existing in the three markers is not linked to the quantitative characteristics studied.