Variabilidade e desempenho forense de microssatélites utilizados na verificação de parentesco do plantel brasileiro de cavalo puro sangue inglês (PSI)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Thoroughbred horses (TB) is a breed derived from a considerably narrow genetic base involving a few founder stallions, displaying today a reduced allelic diversity when compared to other horse breeds. TB animals, however, demand a very high rigor in the genealogical control in view of its international reputation and ample worldwide trading in which Brazil plays an ever increasing role. In this study the forensic performance of a large set of microsatellite markers was evaluated including the nine ISAG recommended loci, 8 widely used complementary loci and the newly proposed battery of TKY markers validates in the 2005-2006 ISAG comparison trials. The forensic performance was evaluated in two samples of Brazilian PSI, one made up of 142 stallions (PSI 142) and the other of 597 mares (PSI 597) that took part in the generation of foals in 2004-2005. Markers in both sets showed ample allelic diversity and high heterozygosity and both loci sets reached a Power of Exclusion (PE) greater than 99,95%. For the TKY loci a very small but significant inbreeding was detected. The nine locus set recommended by ISAG as a minimum set reached a significantly lower PE not only in TB but also in other more diverse horse breeds raised in Brazil. In 23 paternity tests involving both parents and foal in which two isolated inconsistencies in allelic transmission were observed no further exclusions were detected after testing the 13 TKY locus set, therefore validating the original conclusion of qualification. These results provide experimental support to the procedure adopted in our lab to declare a foal as positively qualified as progeny of the tested stallion even when two isolated genotype inconsistencies are observed. Results of a simulation study indicate however, that such a procedure can only be adopted in complete trios when minimum sets of 15 ISAG markers are used and that this procedure is not viable when the dam is not tested, unless very large sets of microsatellites, over 30, are used. Recommendations about how many and which markers use in horse parentage testing depend on many factors. Simple comparisons among common sets of microsatellites should be seen as ad-hoc approaches as alternative solutions can always be suggested varying how many and which loci are used. The results of this study also suggest that sets including 13 TKY loci or sets of 14 loci including the nine recommended by ISAG, complementary markers and a highly informative TKY locus can reach a PE above 99.95%, the ISBC (International Studbook Committee) recommended threshold. The analyses carried out also show that the nine ISAG markers are not sufficient for an adequate paternity exclusion in TB horse. Furthermore the TKY set of markers constitutes an excellent tool for the resolution of more complex situations involving genetically related stallions or when isolated exclusions are detected in routine parentage testing.

ASSUNTO(S)

cavalo de raça microssatélites genética desempenho genetica thoroughbred microsatellites forensic performance

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