IB Inheriting genetic disorders © Oxford University Press 2011 Inheriting genetic disorders
IB 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.
IB Inheriting genetic disorders © Oxford University Press 2011 Genetic diagram showing how polydactyly is inherited
IB 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.
IB Inheriting genetic disorders © Oxford University Press 2011 Genetic diagram showing how CF is inherited