We view a genotype as a vector of sites, each site having a value from the domain {0, 1, 2}; and a haplotype as a vector of sites, each site having a value from the domain {0, 1}. According to Gusfield, a genotype is ambiguous if its value is 2; and resolved otherwise. Two haplotypes h₁ and h2 form (or explain) a genotype g if for every site j the following hold:

if g[j]=2 then h₁[j]=0 and h₂[j]=1;

if g[j]=1 then h₁[j]=1 and h₂[j]=1; and

if g[j]=0 then h₁[j]=0 and h₂[j]=0.

For instance, the genotype 20110 can be explained by the haplotypes 10110 and 00110:

10110

00110

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20110