Question

Study the pedigree chart given below:


What does it show ?

• A. Inheritance of a sex-linked inborn error of metabolism like phenylketonuria
• B. Inheritance of a condition like phenylketonuria as an autosomal recessive trait
• C. The pedigree chart is wrong as this is not possible
• D. Inheritance of a recessive sex-linked disease like haemophilia

Answer 1

The correct option is B Inheritance of a condition like phenylketonuria as an autosomal recessive trait

According to pedigree, offspring of normal parents show the trait which means that the trait is recessively present in the normal parents; the trait is recessive. In a first filial generation, both son and daughter show the trait. As we know that a sex-linked recessive trait can be expressed in either sex (not in both); the X-linked trait is expressed in male progeny while the female progeny serves as a carrier and the Y-linked trait is expressed in sons only. Presence of trait in both son and daughter in F${}_1$ generation confirms that it is an autosomal trait. Hence, the inheritance pattern is autosomal recessive like phenylketonuria.