(a) Haemoglobin is made of two α-globin chains and two β-globin chains. A person may have a mutation in the gene coding for β-globin. This is due to a base substitution and leads to the production of abnormal β-globin and therefore abnormal haemoglobin. A person who is homozygous for the mutant allele will have a condition called sickle cell anaemia.

1. (a)Outline the phenotypic effects of having abnormal haemoglobin in a person with sickle cell anaemia.[4]
2. (b)(i)HbA is the allele coding for normal β-globin. HbS is the allele coding for abnormal β-globin. The alleles are codominant. Explain what is meant by the alleles being codominant.[1]
3. (b)(ii)A person who is heterozygous will have sickle cell trait but may not experience the symptoms of sickle cell anaemia. Suggest why a person with sickle cell trait may not show the symptoms of sickle cell anaemia.[1]
4. (b)(iii)Construct a genetic diagram to show the possible offspring for a man and a woman who both have sickle cell trait. parental phenotype parental genotype gametes offspring genotypes offspring phenotypes[3]