Linkage disequilibrium is defined as the nonrandom association between the alleles of two or more loci. The level of linkage disequilibrium will be greater between S and C loci in case of hepatitis A virus.
In hepatitis B virus, a single genetic segment contains both S and C loci and the recombination between loci S and C are expected to be rare and will result in higher linkage disequilibrium. Both the alleles occur non-independently, which indicates that the value of coefficient of linkage disequilibrium is high.
The influenza virus contains eight separate segments, and the loci HA and NA are present on the different segments [non-homologous chromosomes]. In non-homologous chromosomes, the recombination between HA and NA segment are expected to be high and will result in the low level of linkage disequilibrium. Recombination refers to the exchange of genetic materials between two different segments of the chromosome. In the influenza virus, the alleles occur independently with each other, and in this case, the value of coefficient of linkage disequilibrium is zero.
The higher level of linkage disequilibrium can be seen between S and C loci. Loci S and C are present on single genetic segment, and the recombination between these loci is quite rare, which increases the linkage disequilibrium. On the other hand, the alleles at HA and NA loci occurs independently, giving a low value of coefficient of linkage disequilibrium.