Increased heterozygosity and allele variants are seen in Texel compared to Suffolk sheep

In this study, the Suffolk and Texel sheep breeds were compared for microsatellite marker heterozygosity throughout seven chromosomal regions in the sheep genome. A total of 623 Texel animals and 489 Suffolk animals in five and three half-sib families, respectively, were genotyped for microsatellite markers across the seven different chromosomes. Using the observed allele frequencies, the expected levels of heterozygosity were calculated for each family. The expected levels of heterozygosity did not significantly differ between the breeds across all regions studied. However, levels of expected heterozygosity were 32% higher in Texel animals on chromosome 4 due to a region of increased heterozygosity between BMS648 and BM3212. The number of allelic variants significantly differed between the breeds, solely due to a region of increased number of alleles on chromosome 20. This region of higher numbers of allele variants in the Texel breed extended from the MHC to c. 15 cM distal to the MHC region incorporating markers OMHC1, CSRD226, TGLA387 and BM1818, which had 3.30, 7.02, 3.09 and 6.75 more alleles in Texel than in Suffolk animals, respectively. No difference was observed in the variance of allele frequency between the two breeds. It is proposed that previous selective sweeps may have reduced numbers of alleles and levels of heterozygosity in the Suffolk breed.