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Chimps are our closer relative.

Any genetic similarity between humans and chimps must exist on the common ancestor.

Pig branch out sooner. So, any genetic similarity between humans and pigs must be on common ancestor between humans and pigs. That must be on common ancestor between humans and chimps.

But chimps may evolve differently.

Hmmm... I am confused.

Actually is there any?

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This is a great question. Looking forward to the answers. –  Gabriel Fair Dec 13 '13 at 13:40
    
For those wanting to answer: Here is a closely related question that share many similarities ;) –  Remi.b Dec 13 '13 at 13:52
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2 Answers

Yes there are!

I think it would make more intuitive sense to you if you would have switched the words chimps and humans in your question:

Are there genetic similarity between chimps and pigs that don't exist in humans?

Then, you would directly answer, of course, there are genes concerning bipedalism, brain (FoxP2 for example), digestive track (adult production of lactase for example) and so, and so… which are different in humans but might not have much reasons to be so different between pigs and chimps. Those mutations occured on the human lineage after the split between human and chimps.

To answer your question:

Are there genetic similarity between humans and pigs that don't exist in chimps?

Yes. Most of these difference are due to mutations that occurred in the chimps lineage after the split of the original lineage into human lineage and chimps lineage.

The following are improbable but would also allow to explain such similarities:

  • Horizontal gene transfer between human and pig after humans and chimps lineages splitted.

  • Convergent evolution.

    • Maybe pigs and human got the same beneficial mutation that never appeared in the chimps lineages.
    • Maybe pigs and human, due to the fact that today live in cold climates evolved the sequence ATTCGCTGA which cause them to produce a more efficient shivering!
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This question doesn't make a lot of sense. Humans, chimps and pigs are all eukaryotes, share a lot of sequence similarity due to common ancestry. We are all vertebrates, we are all placental mammals. So there is a lot of similar sequence between us, more than we have with lizards.

So humans, chimps and pigs all have a common ancestor. Is it possible that there are some sequences where the human versions have drifted farther from the common ancestor than either chimps and pigs have? Sure, it's possible but probably not very common.

Here's link to ensembl's page on one random gene, the transferrin receptor. You can see the % identity between the orthologues of a number of species. Chimps and humans are 99% identical. Pigs are 76%. All the primates whose transferrin sequences are known are in the 90's percentage wise, the other mammals are not nearly so close a match.

http://www.ensembl.org/Homo_sapiens/Gene/Compara_Ortholog?db=core;g=ENSG00000072274;r=3:195754054-195782085;t=ENST00000360110

Here's another gene, where the gene has changed much less over time, but pigs are still not as similar to human as chimp

http://www.ensembl.org/Homo_sapiens/Gene/Compara_Ortholog?db=core;g=ENSG00000138379;r=2:190920423-190927455;t=ENST00000260950

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Perhaps what Jim Thio is interested in is the xenografts from pigs to humans.. –  WYSIWYG Dec 15 '13 at 14:06
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