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) = [tex]\frac{\text{ Total favorable outcome}}\text{Total possible outcome}[/tex]
Probability that the child will have beta-thalassemia major =\frac{_{1}^{3}\textrm{C}}{_{1}^{4}\textrm{C}}
=[tex]\frac{3}{4}[/tex]
∴ favorable=[tex]_{1}^{3}\textrm{C}[/tex]
And , Total =[tex]_{1}^{4}\textrm{C}[/tex]
Probability that the child will have no trace of the disease=[tex]\frac{1}{4}[/tex]
