Shared DNA %

Almaviva

Brian Cox telling us there on TV that we share about 99% of our DNA with chimps. Which was the number I probably knew.

But I googled the % DNA shared between sibings, cousins. And the figures quoted are about 50% between siblings, vanishing to negligible for grades of cousins.

Guessing that I am not more closely related to a chip than to my brother though....
What an I missing ?

slowburner

An m.

Capt'n Midnight

the 50% is entire chromosomes matching - this is like getting copies of 01/02/../089/1550 telephone directories from your parents. They have two copies of each with many different years to choose from and it's 50:50 which one they give you.

The 97% is comparing which telephone numbers in the directories have changed compared to other older ones, the older ones would have more changes

Almaviva

Was I comparing apples and oranges?
I was expecting to see a number of 99.manymanynines for the shared DNA between family members if was 98.4% between a human and a chimp. So siblings have DNA 50% identical, and a human and a chimp have 0% identical - but with 98.4% of of the same building blocks?

Almaviva

slowburner wrote: »

An m.

I have it. Just didnt put it in the right sequence....

darjeeling

Almaviva wrote: »

Was I comparing apples and oranges?
I was expecting to see a number of 99.manymanynines for the shared DNA between family members if was 98.4% between a human and a chimp. So siblings have DNA 50% identical, and a human and a chimp have 0% identical - but with 98.4% of of the same building blocks?

Yes, that sounds like it. One figure describes the way relatives are inheriting their DNA, and the other describes how identical it is.

Your father has two copies of each chromosome. Call them A and B. You inherit one complete copy from from him, so overall you inherit 50% of your DNA from your father. What you actually get is a mosaic made from lining the A and B copies up and then swapping segments between them.

Your brother inherits in the same way. But the swap-over sites occur randomly, so where you have inherited a gene from your father's A chromosome, on average your brother has the A copy half the time and the B copy the other half. The same happens with inheritance from your mother. Overall you and your brother coinherit 50% / 2 (from your father) + 50% / 2 (from your mother) of your DNA = 50% in total.

But what we haven't considered is that the genetic sequence of your father's A chromosome actually turns out to be identical to his B chromosome for most of its length. So even when you get your father's A copy and your brother gets the B copy, most often the A and B copies were identical to begin with! This is a consequence of us all being related not all that many generations ago. Or inbreeding, to give it its less polite name.

When you stop considering how you have inherited your DNA and just ask how much of your genome is identical to your brother's or your mother's or father's, you'll find it turns out to be very high - estimated at 99.5% for all of humanity, and therefore higher even than that within most families.

At this point, you can compare the >99.5% figure with the corresponding human vs. chimp figure, which turns out to be somewhere between 95% and 98%, depending on exactly how you do the comparison.

And hopefully no-one can claim recent genetic inheritance from chimps.

locum-motion

Very well explained, Darjeeling.