• Question: how come some characteristics of our ancestors sometimes leave out some generations but go to others? and how does it work when siblings all look different? :)

    Asked by chloebicknell to Ed, Katie, Sam, Steve, Vera on 15 Jun 2011.
    • Photo: Katie Marriott

      Katie Marriott answered on 15 Jun 2011:

      I’m not sure about the first bit of the question.

      The second bit is because there are two parents and so both parents can contribute genes, and not always the same part of the genes – so siblings look different

      Someone else with more knowledge of this area will probably be better at explaining this!

    • Photo: Steven Daly

      Steven Daly answered on 15 Jun 2011:

      DNA is made up from genes, which control everything that goes on in our body. Some of these genes can come in different types, like the gene for eye colour – there is one for blue, a different one for brown, etc. This is the same for most of the genes. There is such a massive number of ways these different genes can be combined, that unless you have an identical twin you will look different to your siblings.

      Also, there is not always one gene for one trait. So for example there is not a gene for being tall, there are many different ones that can contribute. This means that different combinations of the gene types can lead to very different physical appearance.

      As to why characteristics skip generations, I am afraid I do not really know the answer to that one.

    • Photo: Sam Tazzyman

      Sam Tazzyman answered on 15 Jun 2011:

      There are lots of reasons why characteristics can skip generations, all of them to do with the details about genetics. One example is this. A simplified genetic explanation for eye colour is that you have two eye colour genes, one that you inherit from your mother, and one from your father. As Steven said, these genes can either be blue, or brown. The brown eye gene is what we call “dominant”. This means if you have one blue eye gene and one brown eye gene you will have brown eyes. Only if (like me) you have two blue eye genes can you have blue eyes.

      Now here is how a trait like having blue eyes can skip one generation, using my family as an example. My Mum has blue eyes, my Dad has brown eyes. My brother has brown eyes. Now, since Mum has blue eyes, she must have two blue-eyed genes. So she must have passed one of those onto my brother. Since my brother has brown eyes we know he must have at least one brown eye gene, so he must have got that from Dad. So he must have one brown eyed gene (from Dad, who has brown eyes), and one blue eyed gene (from Mum, who has blue eyes) to make up the brown eyes that he has.

      Now, suppose my brother has a child with a blue eyed lady. Then the child would get one blue eyed gene from their mother. They would also get one of my brothers genes. Remember, he’s got one blue eye and one brown eye gene. If he passed on his blue eyed gene then his child would have blue eyes, so the blue eyed gene would have skipped a generation, from my Mum to my brother’s child.

      I hope that you can follow that explanation – sorry if it seems a bit fiddly. A lot of things in genetics are a bit fiddly like that, to do with the details of what genes are inherited when.

    • Photo: Vera Weisbecker

      Vera Weisbecker answered on 15 Jun 2011:

      Sam and Steve explained this really well!

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