Answer:
There are three kind of beta-thalassemia.
Total possible outcome= 3 types of beta- thalassemia + 1 [child will have no trace of disease] = 4
As we know Probability(outcome) =
Probability that the child will have beta-thalassemia major =\frac{_{1}^{3}\textrm{C}}{_{1}^{4}\textrm{C}}
=
∴ favorable=
And , Total =
Probability that the child will have no trace of the disease=