The genetic fault that usually causes colour vision deficiency is passed on in what's known as an X-linked inheritance pattern.
This means:
1) it mainly affects boys, but can affect girls in some cases
2) girls are usually carriers of the genetic fault – this means they can pass it on to their children, but do not have a colour vision deficiency themselves
3) it's usually passed on by a mother to her son – the mother will often be unaffected as she'll normally just be a carrier of the genetic fault
4) fathers with a colour vision deficiency will not have children with the problem unless their partner is a carrier of the genetic fault
5) it can often skip a generation – for example, it may affect a grandfather and their grandson
6) girls are only affected if their father has a colour vision deficiency and their mother is a carrier of the genetic fault
