Genetic Variants in Non-coding DNA
Higher tier only
- During transcription, part of a DNA molecule unwinds, exposing the gene to be transcribed (the gene from which a particular protein will be produced)
- An enzyme known as RNA polymerase then binds to a region of non-coding DNA just in front of this gene
- Non-coding means that the DNA bases do not code for the production of an amino acid
- RNA polymerase makes a complimentary copy of the gene by building a single-stranded nucleic acid molecule known as mRNA (messenger RNA)
- However, genetic variants (different versions of genes caused by mutations) can be produced if a mutation occurs in the non-coding DNA of a gene
- A mutation is a random change to the DNA base sequence
- Such genetic variants can affect phenotype by influencing the binding of RNA polymerase and altering the quantity of protein produced:
- If a mutation happens in the non-coding region to which RNA polymerase attaches, this can affect the ability of RNA polymerase to bind to it
- In some cases, this might make it easier for RNA polymerase to bind. In other cases, it might make it more difficult
- If it makes it more difficult for RNA polymerase to bind, less mRNA will be transcribed from the gene and therefore less protein (that the gene codes for) will be produced
- Depending on the function of this protein, the phenotype of the organism may be affected by how much of it is produced
- In this way, genetic variants in the non-coding DNA of a gene can affect phenotype, even if the coding region of the gene is completely normal
