Question

Which of the following is correct?

• A. Phenylketonuria is an autosomal dominant disorder
• B. Color blindness is a sex-linked dominant disorder
• C. Thalassemia is an autosomal recessive disorder
• D. Cystic fibrosis is an autosomal dominant disorder

Hint:

Autosomal recessive disorders require two defective alleles to express the disease.

Answer 1

The Correct Option is C

Step 1: Understanding genetic disorder classification.
Genetic disorders are classified based on inheritance patterns such as autosomal dominant, autosomal recessive, and sex-linked traits. These patterns determine how a disease is passed from parents to offspring.

Step 2: Concept of autosomal recessive inheritance.
In autosomal recessive disorders, both alleles must be defective for the disease to express. Carriers with one normal allele usually remain unaffected.

Step 3: Evaluating phenylketonuria.
Phenylketonuria (PKU) is caused by mutation in the gene coding for phenylalanine hydroxylase. It is autosomal recessive, not dominant, making option (1) incorrect.

Step 4: Evaluating color blindness.
Color blindness is a sex-linked recessive disorder located on the X chromosome. It is not dominant, so option (2) is incorrect.

Step 5: Evaluating thalassemia.
Thalassemia results from mutations in globin genes affecting hemoglobin synthesis. It follows autosomal recessive inheritance and requires both alleles to be defective.

Step 6: Evaluating cystic fibrosis.
Cystic fibrosis is also an autosomal recessive disorder caused by mutations in the CFTR gene affecting chloride ion transport. It is not dominant.

Step 7: Final analysis.
Only thalassemia correctly matches autosomal recessive inheritance among the given options.