It's Okay To Be Smart

Continuing “Joe’s Answer Bag Week”:

This may be a bold request, but could you post about the percentages of DNA we share with other things? Or a link to something of that nature…
From: chiefsfan71308

Hi there, Chief Sfan (is that Nordic?). I know what you’re getting at with this question. The problem is that you aren’t asking the right one, so I am going to answer it differently. I’ll tell you right away that there’s no master list of How Similar The Human Genome Is To X.
The percentage of DNA that we share with another organism isn’t as important as what that DNA is doing. Because DNA by itself does not an organism make. It’s actually pretty boring stuff just sitting in a nucleus. Of course, if it didn’t do anything, there’d be no nucleus, no cell, no proteins, no organism. It’s the genes that really matter, and more than that? The proteins that they make.
Of the ~3 billion base pairs of DNA in the human genome, only about 1.5% of it codes for proteins (~25,000 genes total, maybe less). The rest? It’s not junk, but it doesn’t produce much of the machinery of life (although it’s really interesting!). A chimpanzee’s genome is about the same size and has just about as many genes. So let’s compare the two, just looking at the genes.

If we took the strings of DNA sequence from our genes and compared it letter for letter with a chimpanzee’s gene sequences, we would find that we share >98.5% of our DNA. What’s more, the proteins made from those genes are 99% identical in the amino acid sequence (because some DNA differences could actually be silent in proteins) meaning that our cells produce almost exactly the same machinery of life. Six percent of human and chimpanzee genes are only present in one species or the other, though. That’s probably a big source of why we’re different (for instance, we have far fewer olfactory genes, so we can’t smell for crap).
SInce chimps and humans diverged from a common ancestor, out genomes have separated by about 1%. Why is all of this important? Well, humans differ from one another by about 0.1% of their gene sequence. We’re pretty diverse in the way we look and function. Chimps and humans differ from each other by about 15 times that. I can believe it. Can you?
Let’s get weirder. About 30% of our genes are totally identical. But some, like a protein called FOXP2, differ in a very particular sequence. What’s special about FOXP2? It’s involved in speech. How different we are is not as important as where we are different. And don’t even get me started on copy number and gene regulation differences!
You can extend this same kind of logic down to mice, dogs, yeast, and even bacteria. It’s all part of a field called comparative genomics, and it’s very, very cool stuff.
A final note: Whenever I write about our genome and how it has evolved, I find it harder and harder to understand why this sort of direct genetic connection scares evolution deniers and creationists so much. There’s great elegance and beauty in how complex our machinery of life has become as species have diverged through time. And there’s a wondrous sense of connection in nature knowing that what makes me alive is not so different from what makes a yeast alive. The small differences that make us human make me feel that much more special, certainly not less so.
For more: Check out the chimpanzee genome project.

This may be a bold request, but could you post about the percentages of DNA we share with other things? Or a link to something of that nature…

From: chiefsfan71308

Hi there, Chief Sfan (is that Nordic?). I know what you’re getting at with this question. The problem is that you aren’t asking the right one, so I am going to answer it differently. I’ll tell you right away that there’s no master list of How Similar The Human Genome Is To X.

The percentage of DNA that we share with another organism isn’t as important as what that DNA is doing. Because DNA by itself does not an organism make. It’s actually pretty boring stuff just sitting in a nucleus. Of course, if it didn’t do anything, there’d be no nucleus, no cell, no proteins, no organism. It’s the genes that really matter, and more than that? The proteins that they make.

Of the ~3 billion base pairs of DNA in the human genome, only about 1.5% of it codes for proteins (~25,000 genes total, maybe less). The rest? It’s not junk, but it doesn’t produce much of the machinery of life (although it’s really interesting!). A chimpanzee’s genome is about the same size and has just about as many genes. So let’s compare the two, just looking at the genes.

If we took the strings of DNA sequence from our genes and compared it letter for letter with a chimpanzee’s gene sequences, we would find that we share >98.5% of our DNA. What’s more, the proteins made from those genes are 99% identical in the amino acid sequence (because some DNA differences could actually be silent in proteins) meaning that our cells produce almost exactly the same machinery of life. Six percent of human and chimpanzee genes are only present in one species or the other, though. That’s probably a big source of why we’re different (for instance, we have far fewer olfactory genes, so we can’t smell for crap).

SInce chimps and humans diverged from a common ancestor, out genomes have separated by about 1%. Why is all of this important? Well, humans differ from one another by about 0.1% of their gene sequence. We’re pretty diverse in the way we look and function. Chimps and humans differ from each other by about 15 times that. I can believe it. Can you?

Let’s get weirder. About 30% of our genes are totally identical. But some, like a protein called FOXP2, differ in a very particular sequence. What’s special about FOXP2? It’s involved in speech. How different we are is not as important as where we are different. And don’t even get me started on copy number and gene regulation differences!

You can extend this same kind of logic down to mice, dogs, yeast, and even bacteria. It’s all part of a field called comparative genomics, and it’s very, very cool stuff.

A final note: Whenever I write about our genome and how it has evolved, I find it harder and harder to understand why this sort of direct genetic connection scares evolution deniers and creationists so much. There’s great elegance and beauty in how complex our machinery of life has become as species have diverged through time. And there’s a wondrous sense of connection in nature knowing that what makes me alive is not so different from what makes a yeast alive. The small differences that make us human make me feel that much more special, certainly not less so.

For more: Check out the chimpanzee genome project.