Use of molecular genetic technologies to characterize the genetic variation in Norwegian and Icelandic cattle
Breed diversity preservation is the essence of animal genetic resources conservation. DNA-based methods, which have been employed to assess genetic diversity, were reviewed. The genetic variation within and among Icelandic cattle and seven Norwegian cattle breeds was assessed from a non-neutral locus (E-locus) plus four microsatellites on chromosome 18 and from other 18 microsatellites. On average 35 (11-46) animals per breed were genotyped. Genetic structure among different colour groups of cattle was assessed using E-locus plus four microsatellites. Contribution of breed to the total diversity and the potential for breed allocation of individual animals were performed. Comparisons of eight different individual assignment methods based on likelihood and distance methods were carried out with these breeds and 28 simulated hybrids using 27 microsatellites. Factors affecting individual assignment success such as, number of loci, sample size, number and divergence of population were assessed. Effect of individual locus variability on assignment success was also assessed. Allelic diversities and mean heterozygosities were more or less similar in the eight breeds but varied considerably among loci. All breeds were at Hardy-Wienberg equilibrium. Differences among breeds ranged from 10% to 16% of total genetic diversity depending on the loci used. Genetic variation among coat colour groups was 8%. The marginal loss of genetic diversity due to hypothetical extinction of a single breed ranged from 13% to 26%. More than 85% of individuals were assigned to the correct breed. Out of the tested assignment methods the Bayesian method was the best. Assignment success was increased with increasing number of loci, sample size and population divergence. Individual locus success rate ranged from 20 to 46%, and was positively correlated with number of alleles and heterozygosity. Besides the genetic contribution of the breed, the conservation priority should consider its social and cultural values, genetic uniqueness, and degree of endangerment, ecological and economical values.
