Practice question

In heterozygous individual carrying one wild-type allele retaining all three restriction sites and one mutant allele lacking recognition site between regions 2 and 3, digestion produces two different fragment lengths spanning probe region due to allele-specific cleavage. Southern blotting with a probe hybridizing between site 2 and 3 detects both alleles because probe sequence exists in both chromosomes regardless of cleavage status. Homozygous wild type would show one smaller band, homozygous mutant one larger band. Heterozygote displays both bands simultaneously, illustrating co-dominance of RFLP markers used in carrier screening and linkage analysis.