Question

Sol.(b) [Key Concept: Huntington's Disease — Autosomal Dominant Pedigree] Huntington's disease is autosomal DOMINANT. If individual 11 is affected (Hh), they must have inherited the H allele from one of their parents (individuals 6 or 7). For this to happen, at least one of 6 or 7 MUST be affected (carry the H allele — Hh). If neither 6 nor 7 is affected (both hh), they cannot pass the H allele to child 11. The pedigree is erroneous because it shows 11 affected without either parent (6 or 7) being affected — this is impossible for an autosomal dominant disorder (assuming unaffected = hh).