This topic summary covers Knowledge Organiser within Inherited Disorders for GCSE Biology. Genetic disorders, family pedigrees, and probability calculations It is section 10 of 11 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 10 of 11
Practice
25 questions
Recall
20 flashcards
Knowledge Organiser
Disorder Comparison
- CF — recessive, allele symbol f, need ff
- Polydactyly — dominant, allele symbol P, need P_
- CF carriers (Ff) — healthy, no symptoms
- Polydactyly carriers — do not exist (they have the condition)
- CF: thick sticky mucus in lungs + gut
- Polydactyly: extra fingers or toes
Punnett Square Probabilities
- Ff x Ff: 25% ff (CF), 50% Ff (carrier), 25% FF
- Pp x pp: 50% Pp (polydactyly), 50% pp (normal)
- Ff x ff: 50% Ff (carrier), 50% ff (CF)
- 1/4 = 25% | 1/2 = 50% | 3/4 = 75%
Common Marks Lost
- Saying carriers are "slightly ill" — they are completely healthy
- Confusing CF (recessive) with polydactyly (dominant)
- Not stating probability as fraction AND percentage
- Forgetting to balance ethical argument — always give both sides
- Not using correct allele notation (f for CF, P for polydactyly)