Explain why some mutations that occur in somatic cells are not inherited by offspring, whereas mutations in germline cells can be passed on to future generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Somatic cells are non‑reproductive body cells that do not contribute to gamete formation.
A mutation in a somatic cell is passed only to daughter cells by mitosis, so it remains confined to a clone of cells in that individual.
Germline cells (cells that give rise to gametes, e.g. in gonads) carry mutations that are incorporated into eggs or sperm.
At fertilisation, a gamete carrying the germline mutation contributes the mutant allele to every cell of the new organism, making the mutation heritable.
A mutation in a somatic cell is passed only to daughter cells by mitosis, so it remains confined to a clone of cells in that individual.
Germline cells (cells that give rise to gametes, e.g. in gonads) carry mutations that are incorporated into eggs or sperm.
At fertilisation, a gamete carrying the germline mutation contributes the mutant allele to every cell of the new organism, making the mutation heritable.
Examiner tips
- Use the terms "somatic" and "germline" cells. Explain the cell‑division processes (mitosis vs meiosis).
- Show the consequence of the mutation being in a gamete for the whole zygote.
Common mistakes
- Confusing somatic and germline cells. Failing to mention that somatic mutations are confined to the individual. Omitting the role of fertilisation in passing the mutation to the next generation.
Mark scheme (4 marks)
- Somatic cells are non-reproductive body cells that do not contribute to gamete formation.
- A mutation in a somatic cell is passed only to daughter cells by mitosis, so remains confined to a clone of cells in that individual.
- Germline cells (cells that give rise to gametes, e.g. in gonads) carry mutations that are incorporated into eggs or sperm.
- At fertilisation, a gamete carrying the germline mutation contributes the mutant allele to every cell of the new organism, making the mutation heritable.
Key terms in this question
somatic cell · germline cell · mutation
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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