The genetic diversity in two local Italian sheep breeds: is selective breeding against scrapie susceptibility possible?

Absztrakt

The genetic variability and presence of population substructures in two conserved native Northern Italian sheep breeds (118 samples), Alpagota and Brogna, not involved into scrapie eradication plans imposed by the European commission (2003), were studied by investigating 17 microsatellite markers. Obtained data were used for computer simulation of successive generations of the two breeds, according to a pattern of within breed crossings and to the choice of breeding males based on the genotypic data for scrapie susceptibility. Assumptions were made for the mating scheme: the allelic frequencies of the sampled individuals are representative of the original populations, all rams and females have the same reproductive performances, males are selected by random drawing and used only for one round of mating, the number of individuals making up the sample population is fixed. Four new subsequent generations were simulated by using two different approaches: discarding males with unfavorable scrapie genotype (Risk Class V) and without selection of the males. The total number of alleles detected in Alpagota was 158 (mean 9.29±2.95), and in Brogna was 186 (mean 10.94±3.05). Differences in the mean number of alleles, expected and observed heterozygosity, and molecular coancestry were not detected for the selected and unselected populations of both breeds. Results show that, if assumptions are met, the selection against scrapie sensitivity is possible in low diffusion local breeds without compromising genetic diversity.