Question

If both parents are carriers for thalassaemia, which is an autosomal recessive disorder, what are the chances of pregnancy resulting in an affected child ?

• A. $25\%$
• B. $100\%$
• C. No chance
• D. $05\%$

Answer 1

The Correct Option is A

 To solve the question of determining the probability of having an affected child when both parents are carriers of thalassaemia, we need to understand the genetics behind autosomal recessive disorders.

Step 1: Understand the Genetics Involved

Thalassaemia is an autosomal recessive genetic disorder. This means that a person needs to receive two copies of the mutant gene (one from each parent) to exhibit symptoms of the disorder. Here are the genetic possibilities for the offspring when both parents are carriers.

• Carrier genotype: \("Aa"\) for each parent, where \("A"\) is the normal allele and \("a"\) is the recessive allele related to the disorder.

Step 2: Set up a Punnett Square

Using a Punnett square, we can calculate the probability of the possible genotypes of the children.

	\(A\)	\(a\)
\(A\)	\(AA\)	\(Aa\)
\(a\)	\(Aa\)	\(aa\)

Step 3: Analyze the Chances

The Punnett square reveals:

• \(25\%\) chance of being \(AA\) (normal and not a carrier)
• \(50\%\) chance of being \(Aa\) (carrier like the parents)
• \(25\%\) chance of being \(aa\) (affected by the disorder)

Conclusion: The chance of the pregnancy resulting in a child affected by thalassaemia is \(25\%\). Thus, the correct answer is \(25\%\).