2.6

Question 0

Haemoglobin is a protein found in red blood cells that

Answer 0

Carries oxygen

Question 1

Sickle-cell anaemia is an inherited condition in which affected individuals produce an

Answer 1

Abnormal type of haemoglobin called haemoglobin S

Question 2

Sickle-cell haemoglobin has a very small difference in the

Answer 2

Order of amino acids in two of the polypeptide chains that make up each molecule

Question 3

As a result of this difference in order of amino acids in two of the polypeptide chains, haemoglobin S is

Answer 3

Less soluble than normal

Crystallises in low oxygen concentrations and become sickle shaped when oxygen is low

Question 4

Sickle shaped cells have difficulty in passing through small blood vessels, so they can block capillaries which means that

Answer 4

Less oxygenated blood reaches affected parts of the body and cells die

Causes damage to tissues and severe pain in the affected individual

Question 5

Sickle cells may block the flow of blood through capillaries in the lungs, causing

Answer 5

• Lung tissue damage (acute chest syndrome)
• Severe pain in the arms, legs, chest and abdomen
• Strokes when parts of the brain tissue die
• Damage to most organs (kidneys and liver)

Question 6

Children with sickle-cell anaemia often suffer damage to the spleen early in life, which leaves them

Answer 6

Vulnerable to certain bacterial infections

Question 7

The sickle-shaped cells are easily damaged and are

Answer 7

Rapidly broken down causing anaemia

Question 8

Anaemia means that the affected person has

Answer 8

Fewer red blood cells

Lower concentration of oxygen in their blood

Question 9

People with sickle-cell anaemia are treated with:

Answer 9

Blood transfusions
Intravenous fluids
Antibiotics
Painkillers

Question 10

However without treatment the condition is usually fatal in

Answer 10

Childhood

Question 11

Sickle-cell anaemia is determined by a single gene with

Answer 11

Two alleles

Question 12

Sickle cell anaemia alleles are not dominant or recessive they are

Answer 12

Codominant

Question 13

Codominant means that

Answer 13

Both alleles contribute to the phenotype in a heterozygous individual

Question 14

Because these Sickle cell anaemia alleles are co dominant the symbol for normal haemoglobin is

Answer 14

HbA

Question 15

Allele for sickle cell haemoglobin is

Answer 15

HbS

Question 16

A person with the genotype HbAHbS is heterozygous and produces

Answer 16

Both kinds of haemoglobin in their red blood cells

Question 17

HbAHbs also means that although they produce both kinds they do not produce enough sickle-cell haemoglobin to show symptoms of sickle-cell anaemia unless they are in conditions where oxygen is limited. These people are said to have

Answer 17

Sickle-cell trait

Question 18

Sickle cell anaemia is very rare in Northern Europeans, but much more common among people in Africa or of

Answer 18

African origin

Question 19

Sickle cell allele is particularly common in parts of Africa and India. These are also the areas where the disease

Answer 19

Malaria is most common

Question 20

In these areas where malaria is most common, people with normal haemoglobin (HbAHbA) do not suffer from Sickle cell anaemia but are more likely to die from malaria. Those with sickle cell trait (HbAHbS) have some protection from malaria so are

Answer 20

More likely to survive, reproduce and pass on their alleles

Question 21

Because natural selection favour heterozygotes in areas where malaria is common, it is inevitable that children with Sickle cell anaemia will be

Answer 21

Born