Question

Which of the following disorders are caused due to recessive autosomal mutations?

• A. Turner's syndrome and sickle cell anaemia
• B. Edward's syndrome and Down's syndrome
• C. Cystic fibrosis and phenylketonuria
• D. Alzheimer's disease and Huntington's chorea.

Answer 1

Answer: (C)

Cystic fibrosis and phenylketonuria

A. Turner's syndrome is produced by the union of an abnormal O egg and a normal X sperm or a normal egg and an abnormal O sperm. The individual has 45 chromosomes (44 + X) instead of 46.

Sickle cell anaemia is caused by a defective allele on chromosome 11. In homozygous condition, the disorder kills the individual. In heterozygous conditions, it leads to haemolytic anaemia under conditions of oxygen 60-70% deficiency.

B. Edward's syndrome is caused due to the presence of an extra chromosome number 18.

Down's syndrome is caused due to the presence of an extra chromosome number 21.

C. Cystic fibrosis is a recessive autosomal disorder which arises due to the alleles present on chromosome 7.

Phenylketonuria is an autosomal recessive disorder in which the homozygous recessive individual lacks the enzyme phenylalanine hydroxylase.

D. Alzheimer's disease is a neurodegenerative disorder caused by the accumulation of amyloid protein plaques in the brain resulting in the degeneration of neurons.

Huntington's disease is an autosomal dominant disorder due to an allele on the short arm of chromosome 4.

Hence, disorders caused due to recessive autosomal mutations are Cystic fibrosis and Phenylketonuria. So, the correct answer is 'Cystic fibrosis and phenylketonuria'.