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Thread: Chimera and odds of getting no dna from a grandparent

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    Chimera and odds of getting no dna from a grandparent

    Created this thread to get this discussion out of the other thread starting on page 17 and going to page 19
    http://www.anthrogenica.com/showthre...worried/page17

    Moderators feel free to move applicable posts to this thread.
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    Hence why I initially edited out chimeras cause it isn't a common thing. Far easier to say some erreonous like great-grandparent when average person has little knowledge even if such happens to be wrong.


    Chimera, in genetics, an organism or tissue that contains at least two different sets of DNA, most often originating from the fusion of as many different zygotes (fertilized eggs).



    In 2003, 26-year-old Lydia Fairchild applied for public assistance in the state of Washington. She had two children already, and a third child on the way. Washington law required that Fairchild submit a DNA sample for the entire family to prove relatedness and to pursue paternal support if appropriate. Those tests confirmed her partner’s paternity, but revealed something unthinkable to her: She was not the children’s biological mother. Lab reports had excluded her genetically as a possible mother.

    Officials called her into the office and badgered her with questions. As she continued to insist she had borne all her kids, they accused her of fraud and threatened to have the children removed by child services. Panicked, Fairchild went home and rummaged for photos and birth certificates as proof, even enlisting the support of the doctor who had delivered the children. She requested retests, but they, too, confirmed that she was not the mother.

    When her third child was born, a court officer was present to witness the birth and an immediate DNA test. When those results, too, showed that Fairchild was not the mother, she was suspected of being some kind of unconventional surrogate.

    Fairchild sought legal assistance but attorneys turned her down, viewing the DNA tests as conclusive proof. Finally, attorney Alan Tindell agreed to take the case. He believed Fairchild’s story, and so he tried to get to the bottom of the mystery. He found his answer in the New England Journal of Medicine. There, doctors told the story of Karen Keegan, a Boston woman in need of a kidney transplant. Her entire family had undergone tests to find a match; the testing revealed that her two sons were not her own.

    Treating it as a “medical mystery,” doctors probed further. They took samples from different parts of Keegan’s body, and even dredged up some old tissue from her thyroid that had been removed in the past. That old thyroid solved the case—it contained DNA that was different from the other parts they had sampled, and that matched her sons’. The study also referenced two other known cases of the kind. Tindell asked for similar testing of Fairchild, which likewise ultimately revealed that she was in fact her children’s mother.
    http://www.thedailybeast.com/article...hetic-dna.html



    One person outside: But two people "inside": That's the gist of the chimera, a human being who carries the DNA (and sometimes the body parts) for two. It sounds crazy, but it happens. In fact, doctors think it probably happens more often than we realize.
    http://boingboing.net/2009/05/01/the...owing-wor.html


    But scientists are discovering that — to a surprising degree — we contain genetic multitudes. Not long ago, researchers had thought it was rare for the cells in a single healthy person to differ genetically in a significant way. But scientists are finding that it’s quite common for an individual to have multiple genomes. Some people, for example, have groups of cells with mutations that are not found in the rest of the body. Some have genomes that came from other people.
    http://www.nytimes.com/2013/09/17/sc...uble-take.html
    Last edited by Calas; 04-19-2017 at 02:05 AM.

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    In this particular story, it seems pretty likely that they weren't doing an autosomal DNA test. They were probably only testing a limited number of markers.

    The reason I say this is that chimeras don't involve the DNA of strangers, but of very close relatives -- in fact, twins. If they'd been doing the kind of autosomal DNA testing done by 23andMe, it would have been immediately obvious that the mother was at least her children's aunt (genetically).

    And if she was genetically their aunt, rather than their mother, her parents would still have had exactly the same relationship to her children: their grandparents. I don't think it would have made any difference in how much DNA they shared with her children.

    My father no doubt would show differences in what DNA he passed on to each of his 10 grandchildren, but probably not huge variations in how much DNA he passed on to his grandchildren. The main difference would likely be that my sisters probably had more crossovers, on average, than my brothers and I did. Therefore, my father might share either a larger or smaller amount of DNA with one of his sons' children, than with one of his daughters' children.

    More crossovers means more recombination. That is, more "chunks" into which the chromosomes are divided, and therefore less average variation in how much DNA from each grandparent on that side is passed to a grandchild. Fewer crossovers means less recombination, and more "intact" chromosomes from just one grandparent. If no chromosome included a crossover, then the DNA of that chromosome would be from just one grandparent. But, the odds would still be very much against all of the chromosomes passed on being from the same grandparent.

    If you assume a 50-50 chance in the case of each chromosome, then it would be akin to tossing a coin 23 times and getting heads each time (or tails each time). That's statistically possible, and even 69 successive tosses ending up with the same face is possible.

    But, I have a hard time accepting a crossover rate of 0 -- especially on three different occasions.

    EDIT: I'd also be wary of articles in the popular press, as opposed to peer-reviewed journals. The former might even sometimes be based on the latter, but they often get important points wrong.
    Last edited by geebee; 04-19-2017 at 04:17 AM.
    Besides British-German-Catalan, ancestry includes smaller amounts of French, Irish, Swiss, Choctaw & another NA tribe, possibly Catawba. Avatar picture is: my father, his father, & his father's father; baby is my eldest brother.

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    The odds of someone not inheriting DNA from their paternal grandparent is, in actuality, about 1 in 200. It isn't the little-green-men DNA as to why you get different locations and even for that matter gain or lack matches among close relatives.

    But as I said via PM.

    I have tested with each company. Each company says I am less than half a full sibling.

    As for the inheritance factor > paternal grandmother does not show up in among their matches. That doesn't mean they didn't necessarily inherit DNA, that means they didn't inherit the right pieces to "show up". I said that from the start I believe in Mitchell's quoted post. Paternal grandmother does not show up.



    I should probably also include the fact that twins happen to run in the family. Paternal grandma was a twin, mum was a twin. And out of my 6 other male siblings, there are 2 sets of twins. Myself & a brother, two identical twin brothers. I haven't tested everyone, I said three siblings [3 + 1 = 4].
    Last edited by Calas; 04-20-2017 at 10:52 AM. Reason: addition of twin

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    Quote Originally Posted by Calas View Post
    The odds of someone not inheriting DNA from their paternal grandparent is, in actuality, about 1 in 200.
    I would like to see the reliable source for this please.

    Blaine Bettinger (probably one of the top 3 experts in the community on the subject) collected data from over 9000 samples and for the grandparent relationship gives average 1765cM with range 1272 to 2365 cM.

    https://isogg.org/wiki/Autosomal_DNA_statistics

    Leah Larkin who is a professional phylogenist gives a range of 18%-32% (taken from the DNA Detectives group).

    http://thednageek.com/the-limits-of-...ips-using-dna/

    Again please, give us a reliable secondary source and explain the apparent discrepancy with the above sources.
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    In the 2012 paper by Ralph and Coop 'The geography of recent genetic ancestry across Europe' [1] they comment

    "theoretical considerations suggest that all humans
    are related genealogically to each other over surprisingly short
    time scales [6,7]. We are usually unaware of these close
    genealogical ties, as few of us have knowledge of family histories
    more than a few generations back, and these ancestors often do
    not contribute any genetic material to us [8]."

    ref [8] is
    8. Donnelly KP (1983) The probability that related individuals share some section
    of genome identical by descent. Theor Popul Biol 23: 3463.

    which you can download a scanned PDF of from

    http://faculty.washington.edu/eathom...p_donnelly.pdf

    If one consults Table 1 in the above it shows 'Probability of no detectable relationship' for values of k where for grandparents k = n+1 in (great)^n grandparent. The first entry they even bother to give is for k=4 ie great great great grandparent and the probability is 0.0001.

    The paper is from 1983 granted but still being cited recently (158 citations on Google Scholar).

    [1] http://journals.plos.org/plosbiology...l.pbio.1001555

    Donnelly_prob_rel.png
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    Quote Originally Posted by MacUalraig View Post
    I would like to see the reliable source for this please.
    Private conversations with Razib Khan and Blaine Bettinger.

    You are aware that there are abnormalities in inheritance? That is where mutations, etc. come from. How son and father through rapid mutation can exist in completely different branches of the same haplogroup. Or do you really think humans are carbon copies of one another?


    Quote Originally Posted by MacUalraig View Post
    https://isogg.org/wiki/Autosomal_DNA_statistics

    Leah Larkin who is a professional phylogenist gives a range of 18%-32% (taken from the DNA Detectives group).

    http://thednageek.com/the-limits-of-...ips-using-dna/

    Again please, give us a reliable secondary source and explain the apparent discrepancy with the above sources.
    Again there are abnormalities in inheritance. [Deleted by Moderator]

    The grandmother is not dad's "mother" but his aunt. That means there's less genetic similarity to begin with. Comprende?
    Last edited by Moderator; 04-21-2017 at 03:20 AM. Reason: Personal attack removed

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    Personal insults are completely unacceptable [Moderator comment: agreed, but this is not the place to respond. Please use the Report Post function for that].

    Now, give us a peer reviewed paper, or if you prefer refute the papers I cited. Private conversations don't cut it.
    Last edited by Moderator; 04-21-2017 at 03:31 AM. Reason: added comment
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    Quote Originally Posted by Calas View Post

    You are aware that there are abnormalities in inheritance? That is where mutations, etc. come from. How son and father through rapid mutation can exist in completely different branches of the same haplogroup. Or do you really think humans are carbon copies of one another?
    Haplogroups? We are not talking about uniparental haplogroups or mutations therein, whatsoever. The topic is '...odds of getting no dna from a grandparent'
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    Last edited by Moderator; 04-21-2017 at 03:22 AM. Reason: quotes deleted text

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