The table below shows some details of three genetic conditions that affect humans.
| Disease | Cause | Rate of cases | Effect |
|---|---|---|---|
| Cystic fibrosis | a recessive allele | 1 in 2,500 people | The mutation prevents a cell membrane protein from transporting chloride ions, causing thick mucus to build up. |
| Familial hypercholesterolaemia | a dominant allele | 1 in 250 people | The mutation prevents the liver from removing low-density lipoproteins (LDL) from the blood. |
| Charcot-Marie-Tooth (CMT) disease | a dominant allele | 15 in 100,000 people | The mutation produces a faulty protein that damages the myelin sheath of peripheral motor neurones. |
There are 56 million people in a country. Calculate the number of cases of CMT disease expected in this country.
Explain why CMT disease can cause difficulty in walking, using the information about its effect from the table.
39 exam-style questions on OCR GCSE Biology 3.1 Coordination and control – the nervous system, covering 3.1.1 Structure of the nervous system, 3.1.2 Coordinated response, 3.1.3 The reflex arc, 3.1.4 Structure of the eye, 3.1.5 Defects of the eye, 3.1.6 Structure and function of the brain, 3.1.7 Difficulties of investigating brain function, and 3.1.8 Limitations in treating nervous system damage. Each one has a worked solution and a mark scheme showing where the marks go.