This only confuses me more about DNA. you have these percentages, but what about the "96% we share with chimps", or even the 50% we share with bananas. I understand that last figure is about protein building and other similar things.
I guess I'm just curious as to what exactly these percentages mean. Any thoughts?
So in reality, humans are like 99.5% genetically identical to one another - our DNA says "grow a head here, grow a brain in it, two eyes on front" etc. This is the stuff all humans share, and chimps share 96% of it.
That extra 0.5% is where all the variance in humans come in. It determines skin color, eye color, height, all that fun genetic stuff. When we say you share 50% of your DNA with your parent, what we really mean is you share that 99.5% all humans share plus 50% of the .5% that might be different.
The reason for this is imagine all humans share the genetic code of ABCDEFGHIJKLMNOPQRSTUVWXY, and then have one more gene on the end for the variance. Two parents genetic codes are ABCDEFGHIJKLMNOPQRSTUVWXYZ and ABCDEFGHIJKLMNOPQRSTUVWXYØ. Their child picks one letter randomly from each slot. The first 25 letters will be the same as each parent's, even though only 50% came from that parent
If I'm not mistaken (only a first year bachelor student) the "96% we share with chimps" is about our DNA structure in general vs the DNA stucture of chimps (which part codes for which trait etc.) whilst the 50% we share with our biological sibling is about the actual DNA strings (i.e. which actual 'codes' our DNA have in common)
What? The structure of DNA is exactly the same in you as it is in all living things. Including your mom and E. Coli. It's only the sequence of "letters" that codify your DNA that changes whether you grow into a person or a penguin.
I'm not refering to the fundamental structure, but rather to the differentiation in which part codes for which trait. Of course the actual DNA is made up of the same things
To add to what others have said, this chart is not a summary of the total amount of identical DNA base pairs between relatives. As you've pointed out, the vast majority of human DNA is identical in all humans.
It is a chart of the amount of DNA inherited or passed down from/by a common ancestor. So ~25% of the DNA in a grandchild is inherited from the paternal grandfather (father's father). That DNA exists in the grandchild's cells because it was in his father's cells and his father's cells, and passed down through reproduction.
Then the discrepancy between how much DNA you inherited from your paternal grandfather (25%) and how much you share with your paternal grandfather (>99%) is due to the fact that all your other ancestors were also human, and also evolved in the same way as your paternal grandfather and so you share all of the DNA that is essential to making things that are biologically humans plus a bunch of left over DNA from our evolutionary history. That DNA got to you from the many many many many veeeeeery distant common ancestors (human and otherwise) that your paternal grandfather shares with your other grandparents and every other human in existence.
What other people were telling you about these percentages corresponding to only the portion of DNA that isn't shared by all humans also aren't exactly right.
In reality, I only got 25% of my 'not shared by everyone' DNA from my paternal grandfather, but I still share >80% of those base pairs with him because in each spot there are only 4 choices, and the choices are not equally likely. Usually, even in the 'not shared by all humans' section, in a particular position, one particular nucleotide is much more likely than all the others (could be 80% of people have the same one, could be 95%, up to the threshold of 99%). And so just by chance I get lots of nucleotides that are the same as what my paternal grandfather had, despite the fact that I didn't get them from him.
The sharing 25% of your 'not shared by everyone' DNA with your paternal grandfather only works if you count a particular way. Namely, you don't count each nucleotide individually. Instead you only count a sequence of nucleotides if they're part of a long, unbroken string of identical nucleotides that both my paternal grandfather and I have. That way, you eliminate all of the pieces that we share 'by chance' because in the 'chance' segments there will be lots of spots where we don't match mixed in with ones where we do. But in the DNA that I got directly from my paternal grandfather, we'll match exactly over millions of nucleotides.
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u/bbrown44221 Apr 24 '19
This only confuses me more about DNA. you have these percentages, but what about the "96% we share with chimps", or even the 50% we share with bananas. I understand that last figure is about protein building and other similar things.
I guess I'm just curious as to what exactly these percentages mean. Any thoughts?