This topic summary covers Knowledge Organiser within Inherited Disorders for GCSE Biology. Genetic disorders, family pedigrees, and probability calculations It is section 9 of 10 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 9 of 10
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)