• Question: What makes an egg cell split to make twins?

    Asked by itssmeemayaa to Amy, Karen, Sarah, Vijay, Will on 19 Jun 2012.
    • Photo: Sarah Martin

      Sarah Martin answered on 19 Jun 2012:

      Hi itssmeemayaa!

      Great question – and one that developmental biologists spend a lot of time studying! The splitting into twins actually occurs after about 5 days when the egg cell has split a few times to make a small bunch of about 100 cells called progenitors. Very rarely, these cells divide spontaneously and randomly to form two embryos instead of just one! Why they decide to do that is not well understood yet, but it has to do with how these cells are arranged in the little bubble that forms the embryo and placenta. If two groups of cells are separated somehow, then two identical baby twins will form!

      Are you a twin?

      🙂 Sarah

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