However, this diagram shows that out of both haemoglobin types, one of the parents has both 'normal' haemoglobin genes, and the other parent has one 'normal' haemoglobin gene (A) and one haemoglobin S gene (S).

This means that the child will now have a 50% chance of carrying both 'normal' haemoglobin genes, and a 50% chance of carrying one 'normal' haemoglobin gene and one haemoglobin S gene.