Describe6 marksChallenge
Sickle cell anaemia is caused by a mutation in the HBB gene, which codes for the beta-globin polypeptide of haemoglobin. The normal allele is HbA and the mutant allele is HbS. Individuals who are homozygous for HbS (HbSHbS) suffer from sickle cell anaemia, while heterozygotes (HbAHbS) have sickle cell trait and are usually healthy. A man and a woman both have sickle cell trait.
Describe the inheritance of sickle cell anaemia in this family. Include:
- the genotypes of the parents and the gametes they produce,
- a genetic diagram (Punnett square) showing the possible genotypes of the offspring,
- the phenotypes of the offspring and their expected ratio,
- an explanation of how the HBB mutation leads to the different phenotypes at the molecular level.