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The third type (kind) of twins

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  • The third type (kind) of twins

    1. One egg and one sperm - identical twins
    2. Two eggs and two sperms - fraternal twins
    3. One egg and two sperms - semi-identical twins

    I have missed on identified existence of the third type of twins, but today news brought a report about the following article from a team of researchers at the Queensland University of Technology.

    http://doi.org/10.1056/NEJMoa1701313
    Molecular Support for Heterogonesis Resulting in Sesquizygotic Twinning
    Michael T. Gabbett, et al.
    The New England Journal of Medicine 2019; 380:842-849
    2019-02-28


    The original article is not available for free. However, the Queensland University of Technology (QUT) has issued an announcement that conveys the results in relatively simple terms:
    https://www.qut.edu.au/research/article?id=140848
    First semi-identical twins identified in pregnancy



    It appears to me that the scenario of semi-identical twins is not only a rare one, but also results in sterility. There is no final data either way, but with the ovaries removed here and ambiguous organs in one of the twins from the other pair, the fertile scenario seems to be unlikely. On the other hand..., if sometimes both twins are fertile, then the genetic genealogy has another special case to consider.


    Mr. W.

  • #2
    In todays news only the second set ever of semi-identical twins have been identified in Australia.

    Comment


    • #3
      Primary sources do include information about the first set of twins.

      QUT summary (URL above) contains “Sesquizygotic twins were first reported in the US in 2007.”

      The published report is referencing
      https://doi.org/10.1007/s00439-006-0279-x
      Vivienne L. Souter, et al.
      A case of true hermaphroditism reveals an unusual mechanism of twinning
      Human Genetics April 2007, Volume 121, Issue 2, pp 179–185


      Warning:
      Please do not attempt to read the full 2007 paper at work or at a public library, since it includes medical images that might make you explain a lot.


      From 2007 abstract
      Traditionally twins are classified as dizygous or fraternal and monozygous or identical (Hall Twinning, 362, 2003 and 735–743). We report a rare case of 46,XX/46,XY twins: Twin A presented with ambiguous genitalia and Twin B was a phenotypically normal male. [----] The twins are chimeric and share a single genetic contribution from their mother but have two genetic contributions from their father thus supporting the existence of a third, previously unreported type of twinning.

      Mr. W.


      P.S.
      I found the today's report very difficult to follow. The only easy parts were about genetic testing (SNPs and such)
      Last edited by dna; 1st March 2019, 01:43 AM.

      Comment


      • #4
        I could see how xx/xy could render them sterile. I don't see how a xx/xx or xy/xy instance would necessarily result in sterility, unless some other mechanism also goes wrong. (Ie they end up XXX or XYY)

        And I kind of doubt enough twins have been sampled to rule out xx/xx or xy/xy being more common (and viable) among twins than they think at present.

        Which isn't to say the multiple sperm/one ova event wouldn't remain pretty rare in it's own right.
        Last edited by bartarl260; 2nd March 2019, 02:31 PM.

        Comment


        • #5
          Originally posted by bartarl260 View Post
          I could see how xx/xy could render them sterile. I don't see how a xx/xx or xy/xy instance would necessarily result in sterility, unless some other mechanism also goes wrong. (Ie they end up XXX or XYY)

          And I kind of doubt enough twins have been sampled to rule out xx/xx or xy/xy being more common (and viable) among twins than they think at present.

          Which isn't to say the multiple sperm/one ova event wouldn't remain pretty rare in it's own right.
          In both cases, the twins are chimeras, and different tests were used to prove that. In the currently reported case, Twin 1 is approximately 50% XX and 50% XY, while Twin 2 is approximately 90% XX and 10% XY (with large margins).

          The authors are fully aware that a sample of 968 twins is small: “Very large samples of twin pairs would be required to estimate the frequency.” In my opinion, since a rather non-standard DNA testing is involved, that is an expensive proposition. I am imaging that until now nobody looked at non-identical twins from such an angle, so they just wanted to establish an initial estimate.


          Mr. W.

          Comment

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