National Geographic

Chimeras and Mosaics: My New York Times Feature on Our Personal Genome*s*

In a mosaic portrait, many tiles, each a little different from the other, add up to an entire person. Genetically speaking, we can be living mosaics, too. As our cells divide, they sometimes mutate, creating distinct populations within us. Many of us carry the genomes of other people inside our bodies.

Scientists have known about these phenomena for a long time, but it was hard to know whether they were more than odd flukes. Now that scientists can sequence genomes from individual cells, they can now start to get at an answer. They are more widespread than was previously thought. The growing significance of chimeras and mosaicist has implications for our sense of genetic identity, as well as for treating diseases. Our many personal genomes are the subject of a feature I’ve written for today’s New York Times. Check it out.

 

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  1. James V. Kohl
    September 17, 2013

    NYT: DNA double take (how people often have more than one kind of DNA in the same body)

    Excerpt: “(Sequencing can be done in as little as 50 hours.) And they’re identifying links between mutations and diseases that have never been seen before.”

    My comment: Since 1927, the only experiment that might have linked mutations to adaptive evolution, did not find any evidence whatsoever of mutation-driven evolution. Since 1992, there has been a model of nutrient-dependent pheromone-controlled adaptive evolution. Scientific support for that mammalian model is found in every experiment done on every animal tested, and scientific support is now being found for that model in experiments done in plants. (Killing soil microbes appears to result in genetically modified plants.)

    Yesterday, researchers reported: “…we identified a network of genes (centered on p53, topoisomerase 1, and olfactory receptors) whose down-regulation caused the cells to replace wild-type cells in vitro and in the mouse embryo—without perturbing normal development. These genes thus appear to fulfill an unexpected role in fostering cell cooperation.”

    The role of the olfactory receptors in cooperation to find food, and the role of olfactory receptors in competition for mates appears to ensure nutrient-dependent pheromone-controlled adaptive evolution by preventing fixation of mutations in the organized genome of species that sexually reproduce.

    Today, evolutionary theorists may continue their attempts to define “mutation” in a way that might make other think the mutations that cause diseases could also cause evolution. If there were no model of nutrient-dependent pheromone-controlled adaptive evolution (since 1992), the theorists might pull off that charade. However, they may still hope to convince enough people to ignore the only model of adaptive evolution, ignore the only experiment that refuted mutation-driven evolution, and ignore the entirety of what is currently known about conserved molecular mechanisms in species from microbes to man.

    Tomorrow, if you are an evolutionary theorist who would rather not examine experimental evidence, please begin telling others how ignoring biological facts might help them to understand behavioral development that is pertinent to evolutionary psychology. But also, start trying to explain to them why you thought the mutations that cause diseases also caused adaptive evolution. There’s never been a biologically-based model for that!

    For a succinct representation of the theory, see “Mutation-driven evolution” (1) Mutation is the source of all genetic variation on which any form of evolution is dependent. Mutation is the change of genomic structure and includes nucleotide substitution, insertion/deletion, segmental gene duplication, genomic duplication, changes in gene regulatory systems, transposition of genes, horizontal gene transfer, etc. (2) Natural selection is for saving advantageous mutations and eliminating harmful mutations. Selective advantage of the mutation is determined by the type of DNA change, and therefore natural selection is an evolutionary process initiated by mutation. It does not have any creative power in contrast to the statements made by some authors.” p 196.

  2. Chris
    September 17, 2013

    It was a very interesting article, and the last few paragraphs made have a wonder about blood tests for genetic sequences.

    My oldest has obstructive hypertrophic cardiomyopathy, which is when the heart muscle starts to grow abnormally any time between birth to at least middle age. My son’s condition was discovered when he was fourteen, so a best guess is that heart muscle started to grow during his puberty.

    It was found because it caused a heart murmur, and the doctor ordered an echocardiogram. Which is fortunate since it is most often diagnosed after “sudden cardiac death.”

    There are (at least last year) eighteen known genetic sequences that cause HCM. They looked for them in his blood, but none were found. Your article made me wonder if they would have found one of those sequences in the heart tissue that was removed surgically last year at the Mayo Clinic. Or it could be just one more unknown genetic sequence, that is possibly de novo (we had family echocardiogram day, and neither us, his parents, nor his sister and brother seem to have HCM).

    Then again, I wonder what happens to cause heart cells to just start growing. Not only do they start to obstruct the aortic valve, and damage the mitral valve with back wash… they also are disorganized causing issues with the electrical conduction, plus it creates scar tissue. I am just a parent, and am relaying what has been told to me.

  3. Andrew
    September 18, 2013

    Good gracious Carl, you find the most amazing stuff.

  4. Daniel Kim
    September 21, 2013

    I greatly enjoyed the article in the Times. I was particularly intrigued by the graphical feature showing patterns of mosaicism, because some of the patterns reminded me of the segmented pattern of Drosophila homeobox gene expression. The picture at (http://free1.ed.gov/images/resources/structure-function.jpg) also shows a similarity that may provide clues about the timing or origins of certain types of mosaicism.

  5. SocraticGadfly
    September 25, 2013

    Couple of questions, Carl.

    First, does the new research indicate a tentative percentage on what proportion of humans are chimeras? I have heard that many conceptions apparently begins as twins, but didn’t know how many of these actually became chimeras, or the percentage number of twin conceptions.

    Second, are chimeras more likely to be same sex than opposite sex? Ditto on twin conceptions.

    [CZ: There haven't been enough large-scale surveys to give a number to your questions.]

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