• Question: when a parent has a specific condition that impedes their life, why does the baby receive this trait, because surely the baby would take the healthy gene from the other parent?

    Asked by XandyisBAE to Gemma on 5 Mar 2018.
    • Photo: Gemma Chandratillake

      Gemma Chandratillake answered on 5 Mar 2018:

      The situation you are describing, where a child inherits a condition, or trait, from a parent like this, is called “dominant inheritance”. We all have *two* copies of each gene, one that we inherit from our mum and the other from our dad. In this case, having a glitch, or mistake, in just one of the parent’s gene copies causes them to have the condition/trait. The other copy of the gene in the parent is fine i.e. works normally. When they have a baby, the child could randomly inherit the gene copy with the glitch/mistake, or the gene copy that works normally from the parent with the trait. They will also inherit a gene copy that works normally from the other parent too. Since in this situation of dominant inheritance, you only need one gene copy with a glitch/mistake in order to have the condition/trait, the child can inherit it from an affected parent. The chance that a child will inherit a dominant condition/trait from a parent is 1 in 2, just like flipping a coin heads or tails, because they could inherit the gene copy with the glitch, or the gene copy that works normally from the parent with the trait.

Comments

  • Photo: Gemma

    Gemma commented on :

    Dominant inheritance is just one way in which conditions/traits are inherited. Some examples of such dominant conditions that we see in families are: hypertrophic cardiomyopathy – a condition that affects the heart and we see affecting different members of a family, down the generations. Another
    really devastating dominant condition that you might have heard of is Huntington’s disease – this is a movie about an 18 year old deciding whether to have genetic testing for this condition that affected her mother: http://twitchdocumentary.com/
    Not all conditions are inherited in a dominant way though. Some conditions only show up if both copies of a gene have glitches/mistakes in them. Such conditions are called recessive. An example is Cystic Fibrosis. For recessive conditions, two parents can each have one gene copy that works normally and one gene copy that has a glitch/mistake. The parents in this case don’t have the trait, but their child could have it if they inherit two gene copies with glitches, one from each parent. The chance for that would be 1 in 4.
    Unfortunately, we don’t get to choose which gene copy we inherit from our parents, we just get one from each randomly depending which copy was in the egg and sperm that came together to make us.
    Eggs and sperm only have one copy of each gene, so that when they come together to make a new person, that person has two copies of each gene again.