Cystic fibrosis is a genetic disease of humans caused by homozygosity for a recessive gene (aa). In a particular large population, the frequency of newborns affected wth cystic fibrosis is 1 in 3,600. In this population, what proportion of marriages between genetically unrelated normal individuals is at risk of producing a child affected with cystic fibrosis? Is it:

1 family in 30

1 family in 300

1 family in 36

1 family in 900

1 family in 15

Cystic fibrosis is the commonest inherited disorder in the UK. One in every 2500 babies is born with cystic fibrosis. One in twenty-five people carry the defective recessive gene. It affects more than 7500 babies, children and young adults in the UK. 14 year old Lauren Hutchins talks about living with the disorder.