IGCSE Biology glossary
Cystic fibrosis
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
A genetic disorder caused by a recessive allele that results in the production of thick, sticky mucus in the lungs, pancreas and other organs. The thick mucus blocks airways, making breathing difficult, and blocks pancreatic ducts, reducing enzyme secretion for digestion.
What to include in an exam answer
Cystic fibrosis is caused by a recessive allele, so both parents must be carriers (or affected) for a child to have it. Use the Punnett square Ff x Ff to show a 1 in 4 chance of an affected child.
Example in context
Using a genetic diagram, show that two carrier parents have a 1 in 4 chance of having a child with cystic fibrosis (3 marks): Parents: Ff x Ff. Gametes: F and f from each. Punnett square gives FF, Ff, Ff, ff. Probability of affected child (ff) = 1 in 4 (25%).
Related syllabus topic
Inheritance