Tuesday, December 09, 2014

King Dick and PCR

The students in my lab course are writing their final exam. Prior to the exam they were given 22 questions and they knew that five of them would be on the exam. I thought that Sandwalk readers might enjoy coming up with answers to some of the questions.
The possible remains of King Richard III of England have recently been discovered. His identity has been confirmed by DNA PCR analysis. Descendants of his mother in the female line have the same mitochondrial DNA as King Richard. However, the results with the Y chromosome were surprising. None of the descendants in the all-male lineage had the same Y chromosome markers as King Richard. This is almost certainly due to something called a "false-paternity" event. (There are other ways of describing this event.) Given what you know about PCR, what are some possible sources of error in this analysis? Would you be prepared to go back in time and accuse one of the Kings of England of being a bastard? [Identification of the remains of King Richard III]
(The lab experiment was to analyze various foods to see if they were made from genetically modified plants.)

Note: It's extremely unlikely that the "false-paternity" event occurred in the lineage leading directly to any of the Kings and Queens of England.


10 comments :

  1. It's extremely unlikely that the "false-paternity" event occurred in the lineage leading directly to any of the Kings and Queens of England.

    Leave it to a Canadian to defend the Kings of England!

    None of the descendants in the all-male lineage had the same Y chromosome markers as King Richard. This is almost certainly due to something called a "false-paternity" event.

    'Twas William Wallace getting horizontal with Princess Isabella of France! Mel Gibson was right! Freedom! Freeedoooom!!!

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    1. I saw the title "King Dick" and thought this post was about Michael Egnor.

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    2. I saw the title "King Dick" and thought this post was about Michael Egnor.

      Only an American would think that another American could be a king. :-)

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  2. The danger of sequencing yourself is ever-present. I hope all the Y-chromosome sequencers were women.

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    1. Yep, I'd guess contamination too. The problem is so common and once it starts it's really difficult to get rid of. It might not even be due to contamination from the person doing the PCR, but from equipment (presumably) used before and not properly cleaned. Something as simple as accidentally dropping and eppendorf tube on a table that haven't been cleaned can contaminate the tube. It only takes a single copy to ruin the whole thing. I get tired thinking about it.

      We had episodes in the lab where ended up moving all the individual stages of preparation for PCR analysis into separate rooms, and we still had contaminations occasionally. Gah. Supposedly there are entire buildings being designed around use for PCR with controlled air-flow directions and stuff like that, to prevent unwanted DNA getting into the labs.

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    2. It's especially a problem with any ancient DNA, where intact copy number in the sample is very low. Richard III counts as ancient DNA, for sure.

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  3. one should be careful about these dna concepts when extrapolating backwards.
    There are options that things might not be so orderly.
    About these recent Kings its okay probably.
    However i know they do crazy dna conclusions about british folks from ancient days.
    Dna is only predicable if there is no mechanism to change it instantly.
    i think there are and so don't score things so confidently.

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    1. So there are mechanism to change DNA instantly? That is what you said, right?

      So now you have change your position of evolution and think it happens and ought to be happening faster than observed?

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  4. "Would you be prepared to go back in time and accuse one of the Kings of England of being a bastard?"

    Is this similar to creating a literature assignment using Josephine Tey's The Daughter of Time to see who killed the Little Princes in the Tower?

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