Explain why two organisms of the same species can show different phenotypes for the same characteristic, such as eye colour.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Genes can exist in different forms called alleles or variants.
Different alleles have slightly different DNA base sequences.
These different sequences code for different proteins or amino‑acid sequences, producing different physical characteristics.
The phenotype is also influenced by the environment, as the genotype interacts with the environment to produce the phenotype.
Different alleles have slightly different DNA base sequences.
These different sequences code for different proteins or amino‑acid sequences, producing different physical characteristics.
The phenotype is also influenced by the environment, as the genotype interacts with the environment to produce the phenotype.
Examiner tips
- Use the term "alleles" and explain they differ in DNA sequence. Mention that different proteins lead to different traits. Include the role of the environment. Keep answer concise to fit 4 marks.
Common mistakes
- Confusing alleles with genes. Forgetting to mention the environment’s influence. Using vague terms like "genetic variation" without linking to DNA sequence.
Mark scheme (4 marks)
- Genes can exist in different forms called alleles / variants
- Different alleles have slightly different DNA base sequences
- Different alleles code for different proteins / amino acid sequences, producing different physical characteristics
- The phenotype is also influenced by the environment / the genotype interacts with the environment to produce the phenotype
Key terms in this question
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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