Crohn’s disease and ulcerative colitis are the two main types of inflammatory bowel disease (IBD). Crohn’s disease can affect any part of the digestive tract, whereas ulcerative colitis is restricted to the colon and rectum.
Scientists investigated the occurrence of these two diseases in twin pairs. Identical twins share 100% of their genetic material, whereas non-identical twins share approximately 50%.
In each twin pair studied, at least one of the twins had been diagnosed with IBD. The table below shows the percentage probability of the second twin developing the disease when their twin has it (the concordance rate):
| Twin type | Crohn’s disease (%) | Ulcerative colitis (%) |
|---|---|---|
| Identical twins | 50 | 18 |
| Non-identical twins | 4 | 4 |
Explain what conclusions can be drawn from the data in the table about the relative influence of genetics and the environment on the development of Crohn's disease and ulcerative colitis.
32 exam-style questions on OCR A A Level Biology Patterns of inheritance. Each one has a worked solution and a mark scheme showing where the marks go.