Genetic variation within the Icelandic cattle breed: assessment using microsatellites and analysis of single nucleotide polymorphisms in the Leptin and DGAT1 genes
Sufficient genetic variation within domestic breeds is a crucial factor in all breeding work. It is a prerequisite for future breeding progress and is used in research and development of breeding methods at the molecular level. The present study estimates genetic variation within the Icelandic cattle breed using two approaches. The data consisted of genomic DNA samples from 100 heifers in first pregnancy collected at 45 dairy farms located in the four major dairy regions in Iceland. First, the samples were genotyped with a set of eleven microsatellite markers and various diversity indices calculated. Second, parts of the Leptin and DGAT1 genes were sequenced in order to search for single nucleotide polymorphisms (SNPs), (several in the Leptin gene and a well known dinucleotide substitution (K232A) in the DGAT1 gene). Polymorphisms in these regions have been identified and associated with commercial traits in different dairy breeds and the purpose was to explore their frequency in Icelandic cattle, as well as to search for breed specific polymorphisms. The Icelandic cattle breed is the only cattle breed in Iceland and has been, more or less, isolated for over 1000 years; therefore it is considered a closed population. Results from the microsatellite analysis revealed a mean number of observed alleles per locus of 6.182, ranging from 4 (ETH3) to 9 (TGLA53) for individual markers. Mean observed and expected heterozygosity were calculated as 0.626 and 0.685, respectively. Polymorphism information content was high ( 0.5) for all the markers indicating that they can be considered suitable for further research of the Icelandic cattle breed and could be adopted for breeding purposes and parentage testing. Average within population inbreeding coefficient of Icelandic cattle ranged between 8.8 and 9.7% for the three approaches applied and the effective number of individuals was estimated to be 111 individuals (lower and upper 95% confidence limits set as 99.76 and 127.39, respectively). No subdivision of the sample was observed and the breed is not likely to have experienced recent bottlenecks. Three out of the five previously known SNPs were identified in the Leptin gene of Icelandic cattle and a new polymorphism, not previously described in other cattle breeds, was found in intron 2. All heifers analysed were homozygous (carrying the GC/GC dinucleotide) for the K232A polymorphisms in the DGAT1 gene. Together, these results indicate a substantial amount of genetic variation within the Icelandic cattle breed despite its long isolation and the progressive breeding strategies used for the population in later decades.
Íslenskar kýr, Erfðabreytileiki, Leptin gen, DGAT1 gen
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