Slashdot Mirror

← Back to Stories (view on slashdot.org)

Semi-Identical Twins Discovered

Posted by kdawson on from the my-brother's-a-keeper dept.

daftna writes in with a story from Nature about a pair of twins who are neither identical nor fraternal: they are semi-identical. Researchers discovered twins who share all of their mother's DNA but only half of their father's. Both children are chimeras — their cells are not genetically uniform, but include a mix of genes from two separate sperm cells that fertilized a single egg. This is, apparently, not as rare as one might think; but the resulting fetus is rarely viable. This report marks the first known incidence of two half-identical twins resulting from a double fertilization.

3 of 224 comments (clear)

  1. Re:Serious question by reverseengineer · · Score: 5, Informative
    Well, this case is primarily interesting in the sense of "this thing that very rarely happens, it just happened." The main scientific benefit is that further light is shed on the mechanisms of human reproduction. Obviously, the outlines of that process are well-known, but there's still a lot of uncharted territory when it comes to the non-normal functioning on this process. Reproductive biology is an area where animal models (even in other primates) tend to translate rather poorly to human beings, and is of course also an area with ethical limits on human experimentation. Conceivably, learning about cases like this can advance knowledge about things like infertility and birth defects.

    There's actually an interesting story, almost the flip side of this rare case in humans, running now in the New York Times about marmosets, in which a form of chimerism is quite widespread:

    One of the most surprising results of the study is that over half of male marmosets have chimeric sperm. Dr. Ross and her colleagues discovered cases in which the DNA of male marmosets turned up in babies supposedly fathered by their fraternal twins. In other words, the sperm came from one male, but it had the DNA of the male's brother. A paternity test would show that the baby's genetic father was actually its uncle. The scientists were not able to isolate DNA from marmoset eggs, but they did find that 2 out of 21 marmoset ovaries were chimeric. It's possible that a female marmoset can give birth to nephews and nieces.
    --
    "FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
  2. Why this is notable: Cortical reaction by wile_e_wonka · · Score: 5, Informative
    I thought I would note why this doesn't happen all the time in humans (in some mammals it is common for an egg to be able to be penetrated by more than one sperm).

    According to my anatomy textbook, after the spem digests its way through the zona pellucida:

    The plasma membranes of the sperm and oocyte then fuse, and the sperm nucleus is engulfed by the oocyte's cytoplasm. This fusion induces the cortical reaction, wherin granules in the oocyte secrete enzymes into the extracellular space beneath the zona pellucida. These enzymes destroy the sperm receptors on the zona pellucida, preventing any other sperm from binding to and entering the egg.

  3. Re:Discovery Health "I'm my own twin" by JeanPaulBob · · Score: 5, Informative

    No, "virgin" was not "indisputably" a mistranslation. And it is most certain that your "young woman" is a poor translation--to my mind, worse than "virgin".

    The issue is not with the New Testament; there is no question that Mary is reported to have been a virgin in the New Testament. The issue originates with the Septuagint, the Greek translation of the Old Testament produced by Jews before the time of Christ, and it has to do with the translation of Isaiah 7:14, an ostensibly Messianic prophecy. (The Septuagint was the translation used by New Testament writers.) It translates the Hebrew "almah" with the Greek "parthenos". Parthenos almost always means "virgin", while almah has a slightly different but overlapping semantic range. It's closer to "maid, unmarried girl, young woman of marriageable age". (Your "young woman" leaves out the unmarried/of marriable age implications.) Culturally speaking, an almah most likely would be a virgin--that would be the strong expectation, and it's enough to make "virgin" a connotation of "almah". While parthenos is not a precise translation, it is not a mistranslation. At the very least, not indisputably so. My goodness, man, just read the Wikipedia entry on almah and follow the references! This is not obscure information.

    Sure, if you limit the meaning of "almah" to "young woman", it makes for a better game of "Hee hee, look at the silly Christians," but if you're interested in honest scholarship, you'll have to open your mind a bit.