What is a SNP?

Getting Started with Genetics Getting Started: Basics of Genetics What is a SNP?

Explaining some terminology…

Half the battle with learning about genetics is understanding the terms. It can be a bit like learning a few words in a foreign language. 

When you start learning about genetics, you will see “SNP” used a lot. (People usually say “snip” for this acronym.)

SNP stands for ‘single nucleotide polymorphism’.  This simply means that one nucleotide in a gene is different from what is typically found in that spot in the sequence. 

Wait –  what are nucleotides? 

Nucleotide bases are the A, C, G, and T’s found in your DNA results. 

“A” stands for adenine, C for cytosine, G for guanine, and T for thymine – these are the nucleotide bases that make up DNA.  

Your DNA is made up of more than 3 billion pairs of these nucleotide bases. (Not all of your DNA codes for genes… later lesson!)

What happens if a change occurs in your DNA? 

Within a gene, if the typical DNA strand calls for an A and you have a G, then this is a change in the DNA that may (or may not) affect the protein that it codes for.

This would be considered a ‘single nucleotide‘ change.

If that change is fairly common, it is called a ‘polymorphism’. Technically, polymorphism means a change found in 1% or more of the population.

Thus, SNP = single nucleotide polymorphism = a change in one A/C/G/T that is somewhat common

What about mutations? 

Mutation is another way of stating that a gene has changed. In research, scientists use the word mutation when the genetic change is found in less than 1% of the population.

Thus, mutations are somewhat rare changes while polymorphisms are more common changes.

Why do Genetic Lifehacks articles refer to everything as a genetic variant? 

Variant is more of a catch-all term, meaning there is a change. This change could be a SNP, a mutation, or that a bit of code is inserted or deleted into the gene.  In general, most of the variants on this website are SNPs.

Example time: When you drink alcohol, your body metabolizes it (breaks it down) using a two-step process. Alcohol is first metabolized into acetaldehyde, and then the acetaldehyde is turned into acetate. The ALDH1 gene codes for an enzyme called aldehyde dehydrogenase. (Note that it ends in “-ase”, so it’s an enzyme).
Check your genetic data for rs671 (23andMe v4, v5; AncestryDNA):
  • AA: Alcohol flush reaction[ref], decreased risk of alcohol dependency
  • AG: Alcohol flush reaction, decreased risk of alcohol dependency
  • GG: typical acetaldehyde metabolism
Members: Your genotype for rs671 is —.
People who have a single nucleotide change at a certain spot on the ALDH1 gene have an A instead of a G at that location. This causes a change in the way the enzyme functions. People with this SNP will notice a tendency to flush when they drink alcohol, especially if drinking a lot or quickly. This SNP causes a change in the aldehyde dehydrogenase enzyme which slows down the conversion of acetaldehyde into acetate. Too much acetaldehyde makes you flush and feel bad. (Acetaldehyde is toxic!) Research shows that people with this polymorphism are less likely to become alcoholics – probably because they feel bad when they drink too much.

To recap: 

  • SNP = single nucleotide polymorphism
  • Polymorphisms are changes occurring in more than 1% of the population
  • SNPs may – or may not – cause changes to the way the protein functions
  • Mutations are changes in a gene. This term is usually used for changes found in less than 1% of the population