# A research team used CRISPR-Cas9 to introduce a loss-of-function mutation into a gene encoding a transcription factor in wheat. Explain why disrupting a gene that encodes a transcription factor is likely to have a more widespread effect on the wheat plant's phenotype than disrupting a gene that encodes a single structural protein.

> OCR A-Level Biology A (H420) — 6.3 Manipulating genomes · Explain · 4 marks

> Transcription factors are proteins that bind to specific regulatory sequences in the genome and control the rate of transcription of target genes. CRISPR-Cas9 is a genome-editing tool that uses a guide RNA to direct the Cas9 endonuclease to a precise location in the genome, where it introduces a double-strand break.

## Mark scheme (4 marks)

1. A transcription factor regulates the expression of multiple target genes simultaneously
2. Loss of the transcription factor therefore means multiple proteins are not produced / multiple biochemical pathways are disrupted
3. A structural protein only contributes to one specific structure or function, so its loss has a limited / localised phenotypic effect
4. Therefore the transcription factor mutation has a more widespread / pleiotropic effect on phenotype because many traits controlled by those target genes will be altered

## Key terms

- [CRISPR-Cas9](https://www.gradenine.co.uk/glossary/crispr-cas9)
- [transcription factor](https://www.gradenine.co.uk/glossary/transcription-factor)
- [loss-of-function mutation](https://www.gradenine.co.uk/glossary/loss-of-function-mutation)
- [structural protein](https://www.gradenine.co.uk/glossary/structural-protein)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-research-team-used-crispr-cas9-to-0402dfed) · Published by Druglandscape Ltd.