Answer:
The correct completion of the text is:
A person who is homozygous for the normal haemoglobin allele (HbA) produces normal red blood cells.
A person who is homozygous for the mutated allele (HbS) produces red blood cells with abnormal haemoglobin, has red blood cells that can form in an altered shape (sickle shape), and has sickle cell anaemia and becomes ill.
A person who is heterozygous has both normal and abnormal haemoglobin in the red blood cells, has sickle cell trait, and is generally healthy but can become ill in certain circumstances (such as oxygen deprivation or stress).
The diagram shows the inheritance of sickle cell anaemia in one family, where:
- HbA represents the normal haemoglobin allele
- HbS represents the mutated allele
- HbAHbA represents an individual who is homozygous for the normal allele (normal red blood cells)
- HbAHbS represents an individual who is heterozygous (sickle cell trait)
- HbSHbS represents an individual who is homozygous for the mutated allele (sickle cell anaemia)
Explanation:
Note: This is an example of autosomal recessive inheritance, where the mutated allele (HbS) only causes the disease when an individual is homozygous for it (HbSHbS). When an individual is heterozygous (HbAHbS), they are generally healthy but can pass the mutated allele to their offspring
