Explain why two organisms that reproduce sexually are unlikely to produce offspring with identical phenotypes to each other.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Sexual reproduction involves the fusion of gametes from two parents. The offspring inherit alleles from both parents.
Model answer (4 marks)
Sexual reproduction creates genetic variation in the offspring.
Each parent contributes one allele for every gene, so the offspring inherit a mix of alleles from both parents.
Because the alleles that are passed on can be different, a range of dominant and recessive combinations can occur, giving different genotypes.
Different genotypes produce different phenotypes, so the physical traits of the offspring are unlikely to be identical.
Each parent contributes one allele for every gene, so the offspring inherit a mix of alleles from both parents.
Because the alleles that are passed on can be different, a range of dominant and recessive combinations can occur, giving different genotypes.
Different genotypes produce different phenotypes, so the physical traits of the offspring are unlikely to be identical.
Examiner tips
- Use the word "genetic variation" early to show understanding of the first point. Show the two‑parent allele contribution to cover the second point. Explain how dominant/recessive combinations give different genotypes for the third point. Link genotype to phenotype for the final point.
Common mistakes
- Confusing a single parent’s contribution with both parents’ contributions. Forgetting to mention dominant vs recessive alleles. Using vague terms like "different traits" instead of "different phenotypes".
Mark scheme (4 marks)
- Sexual reproduction produces genetic variation in offspring
- Each parent contributes one allele for each gene, so offspring inherit alleles from both parents
- Different combinations of dominant and recessive alleles are possible, leading to different genotypes
- Different genotypes result in different phenotypes / the physical characteristics expressed depend on the alleles inherited
Key terms in this question
Related
- All WJEC GCSE Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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