How much Human and Chimp DNA have we compared?

(Dark X Studios) #1

I have found multiple sites that have said we only compared the “non-junk” DNA in Humans with the “non-junk” DNA of the Chimpanzees. Is this true? Or did we compare ALL the DNA of Humans and Chimpanzees?

(Chris Falter) #2

The similarity, generally calculated using Levenshtein distance IIRC, varies depending on whether the non-coding DNA is included or not. If it is excluded, the similarity is 98.5%; if not, the similarity is about 95%.

(Steve Schaffner) #3

It’s false. The whole-genome comparison was done in this paper. Not all of the genome can be sequenced and assembled, but everything that could be, was. That amounted to something over three quarters of the genome. For comparison, only about 10% of the genome is thought to be functional. (Most of what wasn’t compared consists of long stretches of the same sequence repeated over and over again, so it’s not very interesting.)

(Dark X Studios) #4

thanks! This helps a lot

(Dark X Studios) #5

That makes sense. Thanks!

(Dark X Studios) #6

Also, are we talking about Humans or Chimp DNA?

(Chris Falter) #7

Having just perused the paper, I can state that it analyzes both human and chimp DNA. And it does not merely calculate a similarity score; it also draws conclusions about how different kinds of mutations and different kinds of selection pressures have influenced the process of evolution.

I also note that the lead institution of the consortium that published this paper is the Broad Institute, where Steve (@glipsnort) works as a computational biologist.

(Dark X Studios) #8

oh ok. Thanks! I have been confused on the actual percentage of similarity between Human and Chimp DNA

(Curtis Henderson) #9

Roughly 45% of the human genome is repeat sequences, but new discoveries suggest there may be more interesting things going on in there than scientists once thought! Here’s an example:

I’m not making the same argument I’ve heard from ID proponents that interesting functions of non-protein coding DNA disprove evolution, I just think it’s fascinating to see the new discoveries in this area. Each new discovery opens my eyes even more to the amazing creative capacity of our Lord!

(Dark X Studios) #10

Is Chimpanzee DNA the same? Does it repeat like Human DNA?

(Curtis Henderson) #11

Yes, a tremendous amount of repetitive DNA is found in chimp (and other higher ape) genomes. Unsurprisingly, the repeat DNA is similar to the repetitive DNA in the human genome. However, the human genome does contain considerably MORE copies of these DNA sequences.

It is also very interesting to look at HERV (human endogenous retrovirus) sequences in human and higher ape genomes. There are quite a few similarities, but also unique sequences in both human and ape genomes that have arisen after the divergence point from a common ancestor. All a lot of fun to read about and think about!

(Dark X Studios) #12

Alright that’s awesome thanks!! I have to write an Origin of Life paper for Biology at my school and I want to show evidence for Evolution since it is a Christian school and they are mostly anti-evolution.

(Curtis Henderson) #13

Just a caveat… I consider the primary purpose of BioLogos is not to convince everyone that evolutionary creation is “right”, but to demonstrate to both the Christian community and the Scientific community that it is possible to fully accept both genuine Christian faith and conventional science. Good luck on your paper! :slight_smile:

(Allison Garrett) #14

[quote=“cwhenderson, post:9, topic:35717, full:true”]
Roughly 45% of the human genome is repeat sequences, but new discoveries suggest there may be more interesting things going on in there than scientists once thought![/quote]

Just curious, do these repeat sequences serve to provide room for replication errors to occur in erroneous places on the genome?

I do know that even as a padawan Biology jedi, it occurs to me that labeling any part of the genome as “junk” DNA seems unwise given the history of discovery.

(Dark X Studios) #15

Thank! Ya I have been told that. And that is my purpose too. My school generally sees that Evolution cannot fit into a Christian worldview but my goal is to show that it can and that any Christian should never be afraid to ask questions and not be afraid to consider that your interpretation may be wrong. I feel like most young Christians end up leaving the Church because they feel like if they ask questions, others won’t take them serious.

(Curtis Henderson) #16

This is still a pretty sizable mystery in molecular biology. The term “junk DNA” has lost its popularity over the last couple of decades exactly for the reasons you realize. It is fairly likely there are functions that are simply not yet known, instead of summoning the hubris of calling it “junk”.

(Steve Schaffner) #17

I was talking primarily about constitutive heterochromatin, including centromeres and telomeres, not transposons. There are islands of genes in this sequence, but much of it is highly repetitive. A lot is functional in bulk – centromeres and telomeres are both vital – but the details of the sequence don’t matter in the same way that they do for what’s normally classified as functional elements.

ETA: As for things like ERVs, there’s no question that some of them are functional, but they’re likely to be a small fraction of the total.

(Steve Schaffner) #18

There are no doubt functions which we don’t know about, but there are also positive reasons for thinking that most of the human genome has no effect on phenotype. One is the absence of any sign of purifying selection acting of much of the DNA. Another is the argument from genetic load: if the entire genome were functional, almost all mutations would be deleterious; given the mutation rate in humans, roughly speaking that means we’d all be dead.

(Steve Schaffner) #19

The mutation rate probably just scales with the size of the genome, so you’re not really gaining anything by having lots of extra DNA – you just get extra mutations. I’m still perfectly happy to call it junk DNA, by the way. I wouldn’t claim to know for sure whether any particular bit of the genome has no function, but I think it very likely that most of it is junk.

That’s not to say the junk hasn’t had an important role in evolution. Transposable elements, which make up much of the genome and which are the largest source of nonfunctional DNA, are also an important source of new regulatory elements for existing genes, and occasionally of new genes as well. There are intriguing hints that some important evolutionary innovations have relied on the rewiring of developmental pathways by transposable elements. That’s kind of outside my area of expertise, though.

(Steve Schaffner) #20

Yeah, I was an author on that paper. Nothing to do with the actual sequencing, though – I worked on modeling natural selection in humans.