Genetics and Heredity

Practice past-paper questions

Practise O/L exam questions on Genetics and Heredity with worked solutions

1. 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'.
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   (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).
   Source: NIE O/L Science 2022 Paper II Q8

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