Which of the following are Mendelian disorders?
(A) Cystic fibrosis
(B) Phenylketonuria
(C) Adenosine deaminase deficiency
(D) Haemophilia
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (D) only
A Mendelian disorder is caused by a change in a single gene; it passes down by Mendel’s laws and can be traced by pedigree analysis.
(A) Cystic fibrosis — Mendelian. It is caused by a recessive mutant allele of one gene, and NCERT names it among the common Mendelian disorders.
(B) Phenylketonuria — Mendelian. It is an autosomal recessive single-gene disorder; the gene for the enzyme that converts phenylalanine is mutated.
(C) Adenosine deaminase deficiency — Not in NCERT’s list. NCERT discusses it under gene therapy: it is caused by the deletion of the gene for the enzyme ADA, which the immune system needs.
(D) Haemophilia — Mendelian. It is a sex-linked recessive disorder; a single protein of the blood-clotting chain is affected.
NCERT Extract:
Mendelian Disorders – “Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sicklecell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc.”