This topic summary covers Knowledge Organiser within Genetic Inheritance for GCSE Biology. Genetic inheritance patterns, alleles, and inheritance diagrams It is section 8 of 9 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 8 of 9
Practice
25 questions
Recall
25 flashcards
Knowledge Organiser
Key Terms
- Dominant — expressed when one copy present (capital letter)
- Recessive — expressed only when two copies present (lowercase)
- Homozygous — two identical alleles (BB or bb)
- Heterozygous — two different alleles (Bb)
- Genotype — allele combination carried
- Phenotype — observable characteristic
- Carrier — heterozygous, no symptoms, can pass allele on
Must-Know Ratios
- Bb x Bb: 3 dominant : 1 recessive phenotype (3:1)
- Bb x bb: 1 dominant : 1 recessive phenotype (1:1)
- BB x bb: all Bb, all dominant phenotype
- BB x Bb: all dominant phenotype; 50% BB, 50% Bb
- 1 in 4 = 25% | 1 in 2 = 50% | 3 in 4 = 75%
Common Marks Lost
- Not showing gametes in the Punnett square
- Confusing genotype (letters) with phenotype (appearance)
- Saying "dominant = more common" — this is wrong
- Forgetting that probability applies to each child independently
- Using the same letter case for both alleles (e.g., Bb written as bb)