Practise O/L exam questions on Genetics and Heredity with worked solutions
2022 · Paper II · 6 marks
In pea plants, the allele for tall (T) is dominant over the allele for short (t).
(i) Write the genotype and phenotype of a homozygous tall plant.
(ii) Two heterozygous tall plants are crossed. Using a Punnett square, predict the ratio of tall to short offspring.
(iii) Define the terms 'dominant allele' and 'recessive allele'.
Show worked solution
(i) Genotype: TT. Phenotype: tall.
(ii) Cross: Tt × Tt → TT : Tt : tt = 1:2:1. Phenotype ratio: 3 tall : 1 short.
(iii) Dominant allele: the allele that is expressed in the phenotype even when only one copy is present (heterozygous). Recessive allele: only expressed in the phenotype when two copies are present (homozygous recessive).