What does it mean to "share DNA"?

However I want to measure it, that’s what shared DNA between closely related species looks like, eh? Let’s see …

  • I’m told by the best genetic genealogists in the business that modern bona fide, “normal” homo sapiens have four kinds of DNA:
    • autosomal DNA (atDNA) inherited from a male parent and a female biological parent, found in 22 of their normal 23 chromosomes;
    • X-DNA inherited from a female biological parent, and
    • X-DNA inherited from a male biological parent, if they’re female, or Y-DNA inherited from a male biological parent, if they’re male; either of which (X- or Y-DNA) is found in a 23rd chromosome; and
  • some quantity of mitochondrial DNA (mtDNA) inherited only from a female biological parent, which is found, not in the nucleus of the human’s cell at any stage in it’s development from zygote until final and complete post-death deterioriation, if that happens.

If you agree, then I ask you: does the modern, normal chimp genome, have all that?

They sure do, except that chimps (and other great apes) have one more pair of chromosomes than humans do. This is due to a chromosome fusion event somewhere along the lineage that gave rise to humans.

Ahhh, … so you want to play, too, cousin? Okay, get in a bumper-car on the bumper-car court, strap on your seat-belt, put on your helmet, and get ready to roll around a bit.

You say that modern chimps have a pair of chromosomes that humans don’t due to some “somewhat nebulous” theoretical “chromosome fusion event somewhere along the lineage that gave rise to humans.”

Sounds kind of precise to me, but does it really mean that modern chimps and homo sapiens “share the same DNA”? Seems to me that if you have 200 euros (EU) and I have 100 dollars (US), you and I both have money, but we don’t share the same money, do we?

I wouldn’t call them “kinds of DNA” since they all have the same exact chemistry. I would describe it as 4 pools of DNA: non-sex chromosomes, Y chromosome, X chromosome, and mitochondria. What differs between them is how they are inherited.

And yes, chimps have all those same pools of DNA. If we venture farther than the primates into the larger mammal and vertebrate group you would see a number of diverse systems for sex chromosomes and determination of sex.

Now you’re quibbling. But I’ll let it slide for now.
So, chimps and homo sapiens have 4 “pools” of chromosomes in common. Cool! But chimps have more non-sex chromosomes than humans, right? And if I understand Dave Carlson’s link, the hypothesized “chromosome fusion event” was the approximate beginning of the “hominid” (?) line, separating humans and great apes.

Good Lord! Cousin, stay on the bumper-car court. Let’s stick to the post-“chromosome fusion event”.

Yes. Two of those chromosomes fused together in the human lineage. We still have the same DNA, but it’s packaged differently.

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Whoa! now that’s an impressive visual comparison.

This is what the actual human and chimp chromosomes look like next to each other:

It’s tough to see, but the chromosomal banding patterns in chromosome 2 are what you see in the idealized picture from the previous post. If I understand the process correctly, the banding pattern is caused by dyes that prefer A’s and T’s, so regions rich in AT repeats dye more heavily than other areas.


As examples: calyptraeids (slippersnails, Chinese hats and cup-and-saucers) are sequential hermaphrodites, half-grown individuals are male and full-grown are female. They live in stacks of up to 10 (typically) individuals. Then there are the hexaploid-get-two-copies-of-their nuclear-DNA-from-their-mother-and-one-from-their-father organisms, the females-inherit-mother’s-mitochondria-and-males-inherit-father’s, and the massively polyploid sphaeriids (~20x-200x) and ferns (>1000x). There are stranger numbers in certain hybrids, like pentaploid and heptaploid.

I think the original question leads to a male geneticist’s chat up line. ‘Can ah share some DNA with you?’

A simple view is that the extent to which we “share DNA,” or have identical DNA, with another person is a measure of how closely we are related (i.e., have common ancestors).

55% of my DNA matches my brother’s exactly. And my y-chromosome matches hundreds of guys named Talley or Tally or Tolley.


  • “Humans and chimps share a surprising 98.8 percent of their DNA.”

So how many chimps do you have among your DNA matches?

No chimps have shown up on my reports yet. I think there are at least a couple of reasons:

  1. Few, if any, chimps have purchased the tests and
  2. Common ancestors, if any, are so far back in time that the shared DNA doesn’t rise to the reporting level.

Are there any chimps in your matches?

I am no expert in this. I just monkey around with it some.


They have their own sets of tests for relatedness and migration history.

I suppose I should said that chimps haven’t purchased the same tests and I have not joined the same data bases.

It would be interesting to see what happens if you send a chimp’s dna into 23 and me or Ancestory.com. I bet someone has done it. Although, probably would just an inadequate sample reply.

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It appears that 23 and me uses DNA chip technology.

I would suspect that they use stringent conditions for DNA binding, so if the DNA doesn’t match the probes on the chip then you will not get a result. If the chimp DNA is identical to a human variant in the specific regions they are looking at then you would get a result.


Groan. :slightly_smiling_face:  

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None known yet, but I’m keeping an eye on some mischievous knuckle-draggers who’ve been showing up uninvited from time to time.

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