Genotype deduction from dominant inheritance in pedigree

Steps:

• Identify phenotypes: M shows polydactyly (E_), N shows no extra fingers (ee).
• Examine offspring: Presence of both polydactylous (E_) and normal (ee) children indicates M must carry recessive e allele.
• Confirm dominance: E dominant means unaffected offspring from M require M to be heterozygous Ee.
• Rule out homozygous: If M were EE, all offspring would show polydactyly; if both ee, no polydactyly in family.

Why C is correct:

• M (Ee) expresses dominant trait but produces unaffected ee offspring with N (ee), matching Mendelian heterozygous-dominant cross (Ee x ee yields 50% Ee, 50% ee).

Why the others are wrong:

• A: M (EE) would produce only polydactylous offspring, not matching normal children.
• B: Both Ee would yield 75% polydactylous offspring on average, but N lacks trait (must be ee).
• D: Both ee cannot produce any polydactylous offspring, contradicting family traits.

Final answer: C