Question

Study the following and choose the correct statement: I. Sickle cell anemia is due to replacement of glutamic acid in 6th position by valine II. Thalassemia is sex linked disorder due to recessive genes III. Down syndrome is an allosomal disorder IV. Phenylketonuria is due to mutation of the gene-PAH in chromosome 12

• A. I and II
• B. II and IV
• C. I and III
• D. I and IV

Hint:

Down syndrome = Trisomy 21 (autosomal disorder). Phenylketonuria is caused by mutation in the PAH gene on chromosome 12.

Answer 1

The Correct Option is D

Concept: Many genetic disorders arise due to gene mutations or chromosomal abnormalities. To solve such questions, each statement should be examined individually.

Step 1: Analyzing Statement I.
Sickle cell anemia occurs due to substitution of valine for glutamic acid at the sixth position of the beta-globin chain. Therefore Statement I is correct.

Step 2: Analyzing Statement II.
Thalassemia is an autosomal inherited disorder affecting hemoglobin synthesis. It is not sex-linked. Therefore Statement II is incorrect.

Step 3: Analyzing Statement III.
Down syndrome results from trisomy 21. Chromosome 21 is an autosome. Hence Down syndrome is an autosomal disorder, not an allosomal disorder. Statement III is incorrect.

Step 4: Analyzing Statement IV.
Phenylketonuria results from mutation in the PAH gene located on chromosome 12. Thus Statement IV is correct. Hence only Statements I and IV are correct.