Explain how transposons contribute to genetic variation within a population.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Transposons, sometimes called 'jumping genes', are DNA sequences capable of changing their position within a genome. Barbara McClintock first described them in maize in the 1940s, though their significance was not widely recognised until decades later.
Model answer (4 marks)
Transposons can move to new positions in the genome (transposition), which can disrupt or alter the expression of genes at the insertion site.
If a transposon inserts into a coding sequence or a promoter, it can create a loss‑of‑function mutation, producing a new allele and thereby adding genetic variation.
Transposon activity can also cause chromosomal rearrangements such as deletions, inversions or duplications when transposition occurs between non‑homologous sites, further increasing genomic and phenotypic variation.
When these changes occur in germline cells, they are heritable and provide raw material for natural selection to act upon within a population.
If a transposon inserts into a coding sequence or a promoter, it can create a loss‑of‑function mutation, producing a new allele and thereby adding genetic variation.
Transposon activity can also cause chromosomal rearrangements such as deletions, inversions or duplications when transposition occurs between non‑homologous sites, further increasing genomic and phenotypic variation.
When these changes occur in germline cells, they are heritable and provide raw material for natural selection to act upon within a population.
Examiner tips
- Use the word ‘insert’ and ‘disrupt’ to show understanding of transposition. Show that new alleles arise from loss‑of‑function or rearrangement. Mention heritability and selection to link variation to evolution. Keep answer concise and use correct terminology (e.g. ‘chromosomal rearrangements’, ‘germline’).
Common mistakes
- Confusing transposon movement with point mutations. Failing to mention that variation is heritable only if it occurs in germline cells. Using vague terms like ‘change’ without specifying insertion, deletion, inversion or duplication.
Mark scheme (4 marks)
- Transposons can insert into new positions within the genome (transposition), disrupting or altering the expression of genes at the insertion site.
- Insertion of a transposon into a coding sequence or promoter region can cause a loss-of-function mutation, generating a new allele and therefore new genetic variation.
- Transposons can cause chromosomal rearrangements (deletions, inversions, or duplications) when transposition events occur between non-homologous sites, further increasing genomic and phenotypic variation.
- Variation generated by transposon activity is heritable if it occurs in germline cells, providing raw material for natural selection to act upon within a population.
Key terms in this question
transposon · genetic variation
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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