SNPs, CNVs, and our mind-blowing genome

Before we get to SNPs and CNVs, let’s look at some wild facts about the human genome.

Here’s something that is hard to believe.

Ready? The DNA in any two humans is very, very similar – over 99.5% of it is exactly the same.

Wait, really?? YES! Really! (I’m not making this up; see Robbins, page 2).

(Also, our DNA is about 99% the same as chimpanzee DNA, which makes me uncomfortable for some reason.)

But back to the human DNA thing. This incredible genomic similarity between humans means that all our inherited human differences are encoded in less than 0.5% of our DNA. WOW.

So what kinds of variations exist in that tiny amount of DNA? The two most common DNA variations in the human genome are single-nucleotide polymorphisms and copy number variations.

Single-nucleotide polymorphisms (SNPs)

SNPs are DNA variations at one single nucleotide position. They are almost always biallelic, meaning that there are only two possible variant nucleotides in that place (say, A or T). Some SNPs are inherited along with a disease-associated gene (because they are close together on a chromosome) – so some SNPs might turn out to be disease markers.

Copy number variations (CNVs)

CNVs are variations in the number of big stretches of DNA (1000 base pairs to millions of base pairs). One person might have two copies of a particular stretch of DNA, and another person might have 10 copies. Many CNVs are located right in gene-coding regions – so they probably help generate some of the incredible phenotypic diversity that exists in humans.

Yikes. I’m still stuck on the chimp thing.