A blood laboratory compared red blood cells from two patients after placing samples on a microscope slide. Fig. 1 shows the shapes seen. Patient A has the u...
Question 1 Report
A blood laboratory compared red blood cells from two patients after placing samples on a microscope slide. Fig. 1 shows the shapes seen. Patient A has the usual form of haemoglobin. Patient B has sickle cell disease, caused by a change in the DNA base sequence of the gene for haemoglobin. During a long flight, patient B became short of breath because some altered cells reduced blood flow through small vessels.
(a) Describe one difference between the red blood cells from patient A and patient B in Fig. 1. [1]
(b) What is meant by a mutation? [2]
(c) Explain how sickle-shaped cells can reduce the amount of oxygen reaching body cells. [3]
(d) Give one reason why sickle cell disease is described as an inherited disorder. [1]
(e) When both parents are carriers, give the probability that their child will have sickle cell disease. [1]
Answer Details
(a) Patient A's red blood cells are round or disc-shaped, whereas patient B's cells are curved or sickle-shaped. [1]
(b) A mutation is a change in the DNA base sequence of a gene or chromosome. [2]
(c) Sickle-shaped cells are less flexible and may stick together. They can block narrow capillaries, reducing blood flow. Less blood reaches body cells, so less oxygen is delivered to them. [3]
(d) Sickle cell disease is inherited because the allele causing it is passed from parent to child in gametes. [1]
(e) If both parents are carriers, the probability that a child has sickle cell disease is \(25\%\), or one quarter. [1]
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