Pedigree analysis problem with solution (Example 12)

Pedigree analysis problem with solution (Example 12)

Q) Congenital deafness in human beings is inherited as a recessive condition. In the pedigree below, two deaf individuals, each presumably homozygous for a recessive mutation, have married and produced four children with normal hearing. Propose an explanation.

In the pedigree it is given that:

III – 4 and III – 5 (Deaf individual): Having homozygous recessive genotype

Offsprings (IV – 3, IV – 4, IV – 5 and IV – 6): Normal individuals


  • The individuals III-4 and III-5 must be homozygous for recessive mutations in different genes (Simply the trait is controlled by two genes)
  • That means one individual is having genotype aa BB and the other is having genotype AA bb.

III – 4 genotype: AAbb

III – 5 genotype: aaBB

  • mating between III – 4 and III – 5 produces normal offspring
  •  None of their children is deaf because all of them are heterozygous for both genes (Aa Bb).





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