My sister came into town. Now, as siblings go, we look very similar.
Genetically we are said to be 50% similar.
Now I am sure that I read an article in the National Geographic recently that said I was 96% similar to this:
Confused.com (and a little upset quite frankly).
OK, so there is something odd going on here that needs some clarifying. Let’s start by separating the apples from the oranges.
When you hear that we are 96% similar to the great ape species scientists are referring to the fact that we are biochemically that alike. If we are discussing the same ‘fruit’ in terms of siblings, then siblings would be 99.95% similar. This talk of sharing half of your DNA is referring to something else all together.
Let me take it back to basics for you so that it all makes a little more sense. Let’s talk about Genes.
Alright. It might not be a fashionable topic (see what I did there?!) But bear with me. It’s interesting. I promise.
You probably came across the long string of letters that make up DNA during your school days. This alphabet is made up of four different letters, which refers to four types of molecules known as bases. Bases are a type of molecule or biochemical. Is it coming back to you? Remember A,C, T and G?
Do you know the film GATTACA? See what they’ve done there with the title? It’s a section of DNA – genius.
DNA is often referred to as our blueprint. A list of instructions that build who we are. Think of it like the string of letters acting like a code that our cells can read. And this is where genes come in. Genes are specific sequences of DNA in which these instructions lie.
So the sequence, “GACTTAGAGGTTACCTTACATAAGAGCCCTTTGGGACCTT” is an example of a gene.
Each gene has the instruction for one small part of you.
This combination of letters, or gene, codes for a specific protein to be made (this is an over-simplification, but let’s leave it like that or you might throw your computer out of the window). And just to clarify, proteins make up a big percentage of our cells, which make up a big percentage of us.
To summarise…your DNA is a long string of letters and sections of this string make up your genes that contain the instructions to make proteins that makes you your beautiful selves.
Ok, so now the Biology lesson is out of the way let’s get back to my initial point to show how I am really more similar to my sister than an ape/monkey.
When scientists say I am 96% similar to an ape, they are referring to the string of letters in a gene. So, if you compare an equivalent gene between me and an ape that is 1000 bases (letters) long, then 960 bases would be the same. In other words we are 96% biochemically identical.
So what about between humans? The DNA sequences in your genes is on average 99.9% identical to ANY other human. In other words for the same 1000 base gene we talked about, 999 bases would be the same. It is only the remaining 0.1% that is different between humans. This little 0.1% explains all of the variation in hair colour, risks of getting certain diseases etc!
OK, so where does the 50% malarkey come in I hear you cry!
We have just established that your parents, because they are both human (we hope) are 99.9% the same. So, any DNA you get from them is 99.9% the same too, which is also true for your sibling. So, really when we look at how similar you are to your parents and siblings you only need to look at the 0.1% difference.
I’m pretty sure you are aware that you receive half of your DNA from each parent.
So of the remaining 0.1%, 50% of the genes are the same.
The 50% figure refers to the proportion of genes parents and siblings share over and above the average proportion of genes shared by any two unrelated humans. (i.e 99.95% biochemically similar)
Now, since we have 6 billion bases, a 0.05% difference still translates to 3 million differences. Which helps you to explain why you and your sibling are so similar and yet so, so different.
OK, ok. So we are two peas in a pod.
Eye Ball Picture: Image courtesy of aopsan/ FreeDigitalPhotos.net
Darts Picture: Image courtesy of Stuart Miles/ FreeDigitalPhotos.net