Question

Which one of the following pairs is an example of an autosomal recessive disorder?

• A. Phenylketonuria and haemophilia
• B. Colour blindness and haemophilia
• C. Phenylketonuria and thalassemia
• D. Colour blindness and sickle cell anaemia

Answer 1

Answer: (C)

Phenylketonuria is an inborn error of metabolism inherited as an autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result of this, the phenylalanine gets accumulated and is converted into phenyl pyruvic acid and other derivatives. Accumulation of these in the brain results in mental retardation. These are also excreted through urine because of its poor absorption by the kidney.
Thalassemia is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carriers for the gene (heterozygous). The defect could be due to either mutation or deletion which ultimately results in a reduced rate of synthesis of one of the globin chains (a and b chains) that make up hemoglobin. This causes the formation of abnormal hemoglobin molecules resulting in anemia which is characteristic of the disease.