Genetic variants in non-coding DNASpec 3.9B
In short
A genetic variant is a difference in the DNA sequence. A variant in the non-coding DNA in front of a gene can change how well RNA polymerase binds there. More or less mRNA is then made, so the quantity of protein produced is altered, which can change the phenotype. The protein's amino acid sequence is not changed.
A genetic variant is a difference in the DNA sequence. Variants in the non-coding DNA in front of a gene can affect the phenotype without changing the protein itself.
- The variant is in the non-coding DNA, where RNA polymerase binds.
- This can change how well RNA polymerase binds.
- More or less mRNA is made, so the quantity of protein produced is altered.
- The change in the amount of protein can change the phenotype.
Exam tip:A variant in non-coding DNA changes how much protein is made. It does not change the amino acid sequence of the protein.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026
Frequently asked questions
What happens in transcription and translation?
In transcription, in the nucleus, RNA polymerase makes a complementary mRNA copy of a gene, and the mRNA moves out into the cytoplasm. In translation, the mRNA attaches to a ribosome and is read in codons. tRNA molecules bring the matching amino acids, which are linked together to form a polypeptide.
How does the order of bases determine a protein's shape?
The order of bases in a gene decides the order of amino acids in the protein. The amino acid chain then folds in a way that depends on that order, which gives the protein its specific shape. A different order of bases could give a differently folded protein that cannot do the same job.
How can a mutation change a protein?
A genetic variant in the coding DNA of a gene can change the sequence of amino acids in the protein. The polypeptide may then fold into a different shape, so its activity changes. For example, the active site of an enzyme may no longer fit its substrate, and this change can affect the phenotype.
All 4 questions on Protein synthesis and gene variants
