Globin Gene Pathology

Question 1

What is the composition of haemoglobin?

Answer 1

2 alpha chains

2 beta chains

Question 2

How many genes are involved in haemoglobin?

Answer 2

One copy of beta chain on each chromosome

Two copies of alpha chain on each chromosome

Question 3

What percentage of alpha chains would be affected by a mutation of a single alpha gene?

Answer 3

25%

Question 4

What percentage of beta chains would be affected by a mutation of a single beta gene

Answer 4

50%

Question 5

When do beta thalassaemias present?

Answer 5

After birth, as beta chains are not produced until after birth

Question 6

When do alpha thalassaemias present?

Answer 6

Before birth

Question 7

What causes sickle cell disease?

Answer 7

Glutamate to valine substitution at amino acid 6 of the beta chain

Question 8

What is the evidence that the sickle cell variant arose more than once in populations?

Answer 8

Different haplotypes eg Benin, Bantu, Senegal

Question 9

What is a compound heterozygote?

Answer 9

Usually in beta thalassaemias

So many variants that severe sufferers usually have two mutated copies - but two different mutations.