The aim of the present investigation was to evaluate the consequences on the molecular diversity of Sambucana sheep breed (Piedmont, Italy) due to selection on the PRNP gene since 2005. The Sambucana breed had 0.319 and 0.544 allele frequencies for the ARR and ARQ alleles, respectively, before the PRNP selection programme started. It has a limited size (around 3000 animals), and the management of genetic variation is based on a rotational mating scheme. Two groups of 78 and 66 young rams were chosen to be representative of the genetic diversity. The first group included animals born before 2005, the second group included animals born in 2008-2009, after 4 years of selection. The PRNP gene and 14 microsatellite markers were genotyped for all the rams. The microsatellite were recommended by the FAO-ISAG and were considered as selectively neutral. For the PRNP gene, the selection for scrapie resistance increased the ARR frequency to 0.567 and decreased the ARQ frequency to 0.366. The impact of selection on neutral diversity was very low, according to information on the 14 microsatellite markers. Number of alleles, allelic richness, and expected heterozygosity showed no significant differences (t-test) between the two successive groups. The between-group diversity as estimated by the genetic distance of Reynold, appropriated for livestock populations with short-term divergence, was very small. The present investigation provides evidence of no overall genetic differentiation in a short-term perspective. Besides, the change of allele frequencies at the PRNP locus shows that the selection for scrapie resistance was less effective than in other breeds, over a few years.
Impact of selection for scrapie resistance on genetic diversity of the Sambucana sheep breed (Piedmont, Italy)
SARTORE, Stefano;RASERO, Roberto;SOGLIA, DOMINGA;MAIONE, Sandra;SPALENZA, VERONICA;SACCHI, Paola
2010-01-01
Abstract
The aim of the present investigation was to evaluate the consequences on the molecular diversity of Sambucana sheep breed (Piedmont, Italy) due to selection on the PRNP gene since 2005. The Sambucana breed had 0.319 and 0.544 allele frequencies for the ARR and ARQ alleles, respectively, before the PRNP selection programme started. It has a limited size (around 3000 animals), and the management of genetic variation is based on a rotational mating scheme. Two groups of 78 and 66 young rams were chosen to be representative of the genetic diversity. The first group included animals born before 2005, the second group included animals born in 2008-2009, after 4 years of selection. The PRNP gene and 14 microsatellite markers were genotyped for all the rams. The microsatellite were recommended by the FAO-ISAG and were considered as selectively neutral. For the PRNP gene, the selection for scrapie resistance increased the ARR frequency to 0.567 and decreased the ARQ frequency to 0.366. The impact of selection on neutral diversity was very low, according to information on the 14 microsatellite markers. Number of alleles, allelic richness, and expected heterozygosity showed no significant differences (t-test) between the two successive groups. The between-group diversity as estimated by the genetic distance of Reynold, appropriated for livestock populations with short-term divergence, was very small. The present investigation provides evidence of no overall genetic differentiation in a short-term perspective. Besides, the change of allele frequencies at the PRNP locus shows that the selection for scrapie resistance was less effective than in other breeds, over a few years.
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