Key Concept: Alleles control traits, and genetic diagrams predict ratios of offspring.
Section A: Key Terms
1. Define: allele, dominant, recessive. [3]
Section B: Genetic Diagrams
2. Tall (T) is dominant to dwarf (t). Cross Tt x Tt and give the genotype and phenotype ratios. [4]
3. What is the probability of a dwarf offspring from the cross in Q2? [2]
4. Use a genetic diagram for Bb x bb (B = brown, b = blue) and give the phenotype ratio. [3]
Total marks: 12
Mark Scheme
1. Allele = alternative form of a gene; dominant masks recessive; recessive only shows when two copies [3]
2. Genotype ratio 1 TT : 2 Tt : 1 tt; phenotype ratio 3 tall : 1 dwarf [4]
3. $1/4$ or 25% [2]
4. Genotypes 1 Bb : 1 bb; phenotype ratio 1 brown : 1 blue [3]