Abstract :
[en] Quantifying the level of linkage disequilibrium (LD), non-random
association
of alleles at two or more loci, is important to determine the number of markers
needed for genomic selection. The aims of this study were to evaluate the extent
of LD in Dual-Purpose
Belgian Blue (DPBB) and to compare the level of LD in
DPBB with that of Walloon Holstein. Data of 28,427 single nucleotide polymorphisms
(SNP), located on 29 Bos taurus autosomes (BTA), of 639 DPBB and 398
Holstein bulls were used. The level of LD between pairwise SNPs separated by
up to 10 Mb was evaluated, separately for each breed, using the squared correlation
of the alleles at two loci. The analysis of molecular variance showed that
the percentage of variation within populations (85.48%) was higher than between
populations (14.52%). However, permutation tests showed a significant genetic
differentiation between the two studied populations (p < .01). The average LD
found between adjacent SNP pairs in DPBB (0.16 (SD = 0.22)) was generally
lower than in Holstein (0.23 (SD = 0.27)). The proportion of SNPs in useful LD
(r2 > 0.30) within a genomic distance of ≤0.10 Mb between SNPs was 18.58% and
28.23% in DPBB and Holstein bulls, respectively. In both breeds, the effective
population size decreased over generations; however, the decline was greater in
DPBB than that in Holstein. Based on results, it can be concluded that at least
68,000 SNPs are needed for implementing genomic selection in DPBB cattle with
enough accuracy.
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