• Question: is it possible for 2 sperm cells to penetrate a single egg cell? could this be achieved in a laboratory?

    Asked by XandyisBAE to David, Gemma, Matt, Stéphane on 14 Mar 2018.
    • Photo: Stéphane Berneau

      Stéphane Berneau answered on 14 Mar 2018:

      Nice question.
      Two sperms can fertilise an egg. However, this phenomenon is called Polyspermy and it can happen in vivo in the fallopian tubes (where fertilisation occurs). The zygote development will fail.

      Technically, the egg has a mechanism of protection against multiple fertilisation. It is the cortical reaction: vesicles inside the egg near the membrane of the recently fertilised egg will leak their content (protease). The egg membrane is protected against polyspermy.

      Here a video about fertilisation and zygote development (I don’t like the music):

    • Photo: Matt Bawn

      Matt Bawn answered on 14 Mar 2018:

      Hi This is not at all my area, but after a quick google:
      It seems it may be necessary in birds:

      http://rspb.royalsocietypublishing.org/content/282/1818/20151682

      although these seem to be the only reserachers advancing this idea at the moment. I think it will be an interesting thing to keep an eye on.

    • Photo: Gemma Chandratillake

      Gemma Chandratillake answered on 15 Mar 2018:

      If two sperm fertilise an egg, there will be 69 chromosomes instead of 46 (there are usually 23 from the egg and 23 from the sperm). If the zygote doesn’t immediately fail, but instead starts to develop, this can lead to what is known as a partial (or incomplete) molar pregnancy. This is a difficult situation because the embryo is not viable, but there is a risk to the mother, so the tissue has to be removed.
      A “full” molar pregnancy is when the egg, for some reason, has no chromosomes, but is fertilised by one or two sperm. In this case, even though there is the right number of chromosomes, 46, all the genetic material comes from the dad, none from the mum, and this doesn’t work to make a baby (the chromosomes have epigenetic marks depending which parent they came from and you need one set from each for an embryo to develop properly). In this case, again, there is a risk to the mother, so any tissue that grows, has to be removed.
      About 1 in 1000 pregnancies are molar. This is a really horrible situation for those who have go through it, because they have to terminate the pregnancy and then be monitored for cancer before trying again: https://www.mayoclinic.org/diseases-conditions/molar-pregnancy/symptoms-causes/syc-20375175

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