Here's how it works:
* DNA sequence: The DNA sequence contains the instructions for building proteins. Each three-letter "codon" in the DNA sequence codes for a specific amino acid.
* Synonymous polymorphism: A synonymous polymorphism occurs when a single nucleotide is changed within a codon, but the change does not alter the amino acid that is encoded. This is because the genetic code is redundant, meaning that multiple codons can code for the same amino acid.
* No change in protein: Since the amino acid sequence remains the same, the resulting protein is identical to the original version.
Example:
Consider the following:
* Original DNA sequence: GGA (codes for the amino acid glycine)
* Synonymous polymorphism: GGG (also codes for glycine)
Even though the DNA sequence is different, both sequences code for the same amino acid (glycine). Therefore, the protein produced will be identical in both cases.
Implications of Synonymous Polymorphisms:
While synonymous polymorphisms don't directly alter the protein sequence, they can have indirect effects:
* mRNA stability: Some synonymous polymorphisms can affect the stability of the messenger RNA (mRNA) molecule, which can influence the amount of protein produced.
* Splicing: They can sometimes affect the splicing process, which is how introns (non-coding regions) are removed from mRNA before translation.
* Regulation of gene expression: Synonymous polymorphisms can affect the binding of regulatory factors to the mRNA, influencing gene expression levels.
In summary:
Synonymous polymorphisms are DNA sequence variations that don't change the protein sequence but can have indirect effects on mRNA stability, splicing, and gene expression. They are often considered less impactful than non-synonymous polymorphisms, but their effects can be significant in certain situations.