Which of the following conditions show recessive pattern of inheritance?

A. Down’s syndrome

B. Cystic fibrosis

C. Haemophilia A

D. Xeroderma pigmentosum

E. Huntington’s disease

Answer

A. Down’s syndrome – False. Down’s syndrome is caused by trisomy 21, an extra copy of chromosome 21, and is not inherited in a recessive pattern.

B. Cystic fibrosis – True. Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene.

C. Haemophilia A – True. Haemophilia A is an X-linked recessive disorder.

D. Xeroderma pigmentosum – True. Xeroderma pigmentosum is an autosomal recessive disorder caused by mutations in genes involved in nucleotide excision repair.

E. Huntington’s disease – False. Huntington’s disease is an autosomal dominant disorder.

Note

Autosomal recessive disorders

• Oculocutaneous albinism
• Alkaptonuria
• Bartter’s syndrome
• Cystic fibrosis
• Gaucher’s disease
• Glycogen storage disease
• Phenylketonuria
• Wilson’s disease
• Hereditary haemochormatosis
• Xeroderma pigmentosum

X-linked recessive disorders

• Red-green colour blindness
• Non-specific X-linked mental retardation
• Duchenne muscular dystrophy
• Becker muscular dystrophy
• Haemophilia A (factor VIII)
• Haemophilia B (factor IX)
• X-linked ichythyosis
• X-linked agammaglobulinaemia