• Question: We are learning about genes in class, and I was wondering how twins can look different when the same cells were involved in making them?

    Asked by emma007 to Chris, Kay, Kerstin, Lorna, Liv on 16 Mar 2010 in Categories: .
    • Photo: Kerstin Zechner

      Kerstin Zechner answered on 16 Mar 2010:

      In identical twins, the differences can mainly be explained by environmental variations. One twin may, for example, be positioned in the womb better than the other and therefore weigh more at birth and in later development. There are also fraternal twins, which is when two eggs are fertilised by two different sperm during the same ovulation cycle. In this case the twins aren’t identical and don’t look as similar.

    • Photo: Olivia Hibbitt

      Olivia Hibbitt answered on 17 Mar 2010:

      Hi emma007

      A question close to me…..I had twins last year! My twins are fraternal twins, that means they came from two different eggs, so they are basically like brother and sister. Identical twins happen when one fertilised egg splits into two so the genetic material is essentially exactly the same…..so they should be identical!!! That’s the theory, but if you know identical twins you’ll know that often they do look slightly different and that is because we now know that changes happen to genes AFTER fertilisation! This is called epigenetics and it basically means that things that happen during your life can effect the way genes are expressed which gives identical twins very subtle differences in the way they look. This can happen even when they are still developing in the uterus…differences in growth, amount of nutrients they get can have effects on the way genes are expressed. It’s a REALLY interesting area!!

    • Photo: Kay Penicud

      Kay Penicud answered on 18 Mar 2010:

      Non-identical twins don’t actually come from the same cells. Sometimes it can happen that a women has two eggs released into her womb at the same time and they can be fertilised by two separate sperm. so two totally different babies happen to grow in the same place at the same time!

      Identical twins happen when a fertilsed eggs splits into two at the very earliest stages of pregnancy, when its just a ball of cells. Identical twins can look a little different because of environmental factors- maybe one spent a bit longer in the sun and has a few more freckles!

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