• Question: will diseases be in evry person in the family if someone gets a disease?? wuz

    Asked by wuzzy to Alex, Amy, Andy, Georgia, Ollie on 12 Jun 2011.
    • Photo: Ollie Russell

      Ollie Russell answered on 10 Jun 2011:

      Diseases have different causes, some can happen at random or because damage is caused to your body such as lung cancer from smoking or liver disease from drinking too much alcohol. These random diseases shouldnt be passed on to anyone else in the family.

      For a disease to be passed on a persons sperm or egg needs to become damaged. This is normally caused when the DNA in these cells is mutated. When the mutated egg or sperm goes on to make a baby, the mutation is passed on to the child. Some mutations can affect a child if just one of the parents has the mutation, but some need both of the parents to have the mutation in their egg and sperm.

      This child will have the mutation in everyone of their cells, so if they have a child, it is likely that their child will also have the mutation.

      Diseases that can be passed from parent to child are called familial diseases as they can affect whole families.

    • Photo: Andy MacLeod

      Andy MacLeod answered on 12 Jun 2011:

      No, not everyone. It depends on the disease, but ultimately it’s a matter of probability and chance.

      Hi Wuzzy. There are some diseases called “Mendelian” disorders, after Gregor Mendel, a Bavarian monk in who first worked out the basic principles of heredity in the nineteenth century. These diseases follow a simple inheritance pattern, and can be divided into two major classes: Dominant and Recessive. Everyone inherits two copies of each gene, one from mum and one from dad. Recessive diseases, like Cystic Fibrosis, need two mutated copies, so only people who inherit a mutated version from each parent will get the disease. Dominant diseases, like Huntington’s disease, need only one mutated copy – so it comes from either mum OR dad. Even then, it’s still a matter of chance whether the children get the disease.

      If we call the two versions of the Cystic Fibrosis gene ‘C’ for the normal copy, and ‘c’ for the mutated version, then most people in the population will be CC – they will have two normal copies. There are a few people who will be Cc, who carry one mutated copy but don’t have the disease. If two carriers have children together, the chance of each of them passing on their mutated copy is 1/2. So the chance of both of them doing that is ½ x ½ = ¼. So each child of a pair of carriers has a 25% chance of getting the disease, but not all of the children will do so.

      Huntington’s is different. Let’s call the mutant disease causing version ‘H’ , and the normal version ‘h’. Again, the disease is quite rare, so most people will be hh. However, people who develop Huntingdon’s will be Hh. If they have children, assuming their partner doesn’t also have the disease, the probability of them passing on their mutated version is 50%. So if one of your parents develops Huntington’s there’s a 50% chance that you will too. And because the symptoms only come on later in life, it’s impossible to know without a genetic test. (If you watch House, that’s just what happened to Thirteen in a recent series)

Comments