How It Works: Inheriting CF and Polydactyly
Part of Inherited Disorders — GCSE Biology
This how it works covers How It Works: Inheriting CF and Polydactyly within Inherited Disorders for GCSE Biology. Genetic disorders, family pedigrees, and probability calculations It is section 4 of 11 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 11
Practice
25 questions
Recall
20 flashcards
How It Works: Inheriting CF and Polydactyly
Cystic fibrosis (CF) is caused by inheriting two copies of a faulty recessive allele (ff). The faulty allele codes for a defective version of the CFTR protein, which is responsible for controlling the movement of chloride ions across cell membranes. Without functional CFTR, cells cannot regulate water movement properly, so mucus becomes abnormally thick and sticky. This mucus blocks airways in the lungs, making breathing difficult and creating an environment where bacteria thrive. It also blocks ducts from the pancreas, preventing digestive enzymes from reaching the small intestine.
Because CF is recessive, carriers (Ff) produce enough functional CFTR from their one dominant allele to remain unaffected. Only individuals who inherit two recessive alleles (ff) — one from each carrier parent — develop the condition. When both parents are carriers, each pregnancy has a 1 in 4 (25%) chance of producing an affected child.
Polydactyly is caused by a dominant allele (P). Only one copy of the dominant allele is sufficient to produce extra digits. If one parent is heterozygous (Pp), each child has a 50% chance of inheriting the P allele and therefore the condition. A homozygous dominant individual (PP) would pass the allele to all offspring, but this is rare since most affected individuals are heterozygous.