Answer:
Population structure due to the geographic distances that separate both countries
Explanation:
Linkage disequilibrium (LD) can be defined as a non-random association between different alleles (loci) observed in a population. The loci are in LD due to the observed frequencies are statistically higher or lower than it is expected if these nucleotide sequences were independent. LD may be due to different factors which include non-random mating, recombination, genetic drift and population structure.