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Question
In a couple, both male and female were diagnosed to be carrier of the thalassaemia trait. Why were they advised to go to a counsellor? How do you think the counsellor explained them about the probabilities their children being carriers or affected in any way? Explain with the help of a chart if only one of the parents is carrier.
Explain
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Solution
Genetic counselling helps the couple understand the inheritance pattern and the chance of an affected child, and discuss testing and reproductive options. Let T represent the normal allele and t the recessive thalassaemia allele.
When both parents are carriers: Tt × Tt
| Genotype | Outcome | Probability |
|---|---|---|
| TT | Unaffected, non-carrier | 25% |
| Tt | Carrier (thalassaemia trait) | 50% |
| tt | Affected (thalassaemia major) | 25% |
If only one parent is a carrier and the other is non-carrier: Tt × TT
| Genotype | Outcome | Probability |
|---|---|---|
| TT | Unaffected, non-carrier | 50% |
| Tt | Carrier | 50% |
| tt | Affected | 0% |
These probabilities apply independently to each pregnancy.
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