1. IB2.28.4 Inheriting genetic disorders © Oxford University Press 2011 Inheriting genetic disorders

2. IB2.28.4 Inheriting genetic disorders © Oxford University Press 2011 How polydactyly is inherited  The condition is caused by a faulty dominant allele.  This means you have the condition even if you only have one faulty allele.  If one parent has it, then each child has a 50% chance of inheriting it.

3. IB2.28.4 Inheriting genetic disorders © Oxford University Press 2011 Genetic diagram showing how polydactyly is inherited

4. IB2.28.4 Inheriting genetic disorders © Oxford University Press 2011 How cystic fibrosis (CF) is inherited  CF is caused by a faulty, recessive allele of the gene for the cell membrane channel protein.  A person with the disorder has to inherit two copies of the recessive allele – one from each parent. The parents may not have the disease; they may be symptomless carriers. They will each have one recessive allele and one normal, dominant allele. So they have enough functioning cell membrane channels.  At each pregnancy for two carrier parents, there is a 25% chance that the child will have CF.

5. IB2.28.4 Inheriting genetic disorders © Oxford University Press 2011 Genetic diagram showing how CF is inherited