Creative Destruction

March 28, 2007

Just to add to the confusion…

Filed under: LGBT Issues,Science — Daran @ 7:32 am

Geneticists report ‘semi-identical’ twins:

Geneticists in the US have discovered a previously unknown kind of twins they have called semi-identical. The twins are identical on their mother’s side, but only share half of their father’s DNA.

OK, but then they say:

The twins are technically chimeras: that is, their cells are not genetically uniform. Some cells contain male cells with an X and Y chromosome, others have female cells bearing a double load of Xs. In the journal Human Genetics, the researchers report that the proportion of XY and XX cells varies depending on the kind of tissue being examined.

For the genes to be distributed in this way, two sperm cells must have fertilised a single egg. Some DNA from each sperm is present in each child.

That would make them identical twins surely? If each twin got the dna from a different sperm, then they’d be half-identical.

Or perhaps the proportion of cells of one type and the other varies from twin to twin as well as from tissue to tissue.

First, two sperm must fertilise a single egg. This does happen in about one percent of human conceptions. More often than not the fertilised egg does not form a viable embryo. This embryo must then split to form twins, who if they are to be identified as semi-identical, must subsequently come to the attention of scientists.

The Chimera aspect of this is more interesting than the twinning. For example, what would happen if the sperm were from two different men? Can a person have two fathers? Who would pay child support?

11 Comments »

  1. Wow!

    Comment by ohwilleke — March 28, 2007 @ 3:43 pm | Reply

  2. Cool. Don’t some societies have a concept of “partial fatherhood”, in which it is believed that more than one man can be the father of any given child? (Presumably all men who have slept with the child’s mother take some responsibility for any children who show up.) Looks like it might be more possible than one would have thought.

    Comment by Dianne — March 28, 2007 @ 4:37 pm | Reply

  3. There are also “chimaeras” who occur when “fraternal twin embryos” merge early on in gestation. I have seen them featured in episodes of House and Strong Medicine.

    Comment by Glaivester — March 29, 2007 @ 12:51 am | Reply

  4. There are also “chimaeras” who occur when “fraternal twin embryos” merge early on in gestation.

    Yawn. Happens all the time. (Well, frequently enough that no one publishes case reports on it.) So, if life or human life begins at conception, should the chimeras be arrested at birth on charges of having murdered (and eaten!) their twins?

    Comment by Dianne — March 29, 2007 @ 10:12 am | Reply

  5. No, the fetus is too young to be culpable. Instead, the mother should be charged for failure to protect. ;)

    Comment by Robert — March 29, 2007 @ 10:44 am | Reply

  6. Dianne wrote:

    if life or human life begins at conception, should the chimeras be arrested at birth on charges of having murdered (and eaten!) their twins?

    Yes, of course. The state could merge the prison system with hospital materity wards. Someone then hangs a sign: “Welcome to life. Here’s your cell.”

    Comment by Brutus — March 29, 2007 @ 10:45 am | Reply

  7. There are also “chimaeras” who occur when “fraternal twin embryos” merge early on in gestation.

    How many souls do they have?

    What about This duo? All kinds of ethical, legal, and conceptual problems here. For example, what if they became pregnant, and one wanted an abortion but the other didn’t? Whose choice would prevail?

    Comment by Daran — March 29, 2007 @ 11:35 am | Reply

  8. Brutus and Robert, even through the tubes of the internet, I sense a certain sarcasm in your answers…So if you don’t like the legal system for sorting out this problem, how about the medical system? A sufficiently large bribe (aka grant) would convince a number of researchers to look into the problem and attempt to find ways to prevent chimerism from occuring (or, more bluntly, to stop one “baby” from eating the other). Surely that would be a good thing, right? Any number of deaths at a young age might be avoided. Robert’s rich, maybe he could endow a fund.

    Comment by Dianne — March 29, 2007 @ 1:50 pm | Reply

  9. Rich in spirit, maybe.

    Comment by Robert — March 29, 2007 @ 2:05 pm | Reply

  10. And even THAT won’t get me satisfaction. ;)

    Comment by Robert — March 29, 2007 @ 2:05 pm | Reply

  11. Wait for this in the next episode of House on Fox. This research is unique and very interesting. It implies that cells with different genetic codes can in fact coexist peacefully in the same body. Very interesting.

    Comment by Vilon — April 12, 2007 @ 3:15 pm | Reply


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