Beta Thalassaemia Inheritance Probability

Beta thalassaemia is an autosomal recessive genetic disorder. This means an individual needs to inherit two copies of the altered gene (one from each parent) to have the condition, known as beta thalassaemia major.

A 'carrier' of the beta thalassaemia gene has one normal gene and one altered gene. They typically do not exhibit severe symptoms but can pass the altered gene to their children. If both parents are carriers, they each have the genotype $Aa$ (where $A$ is the normal allele and $a$ is the beta thalassaemia allele).

Punnett Square Analysis

To determine the probability for each pregnancy, we can use a Punnett square:

Offspring Genotypes and Risks

• $AA$ (25%): Child inherits a normal gene from both parents. The child will be unaffected and not a carrier.
• $Aa$ (50%): Child inherits one normal gene and one altered gene. The child will be a carrier like the parents.
• $aa$ (25%): Child inherits the altered gene from both parents. The child will have beta thalassaemia major.

Therefore, in each pregnancy, there is a 25% chance that the child will inherit the beta thalassaemia major condition ($aa$).