Genetic testing: prediction vs. risk

Published on May 31, 2020   29 min

Other Talks in the Series: Introduction to Human Genetics and Genomics

Hi, my name is Giles Yeo, and I'm a geneticist based at the University of Cambridge. This lecture is entitled 'Genetic Testing: Prediction vs Risk'. We'll go into why I'm talking about this in a moment, but in effect we're talking about what genetic testing can tell you and how much of genetic testing is predictive, meaning that given a specific genotype you can predict a specific phenotype or a specific disease, and how much of it is just speaking about risk. We'll go through this as the lecture goes on.
Whenever we think about genetics, we think about Mendel and his peas. Mendel was an Austrian monk who was growing peas and trying to figure out what was responsible for the peas having specific colours. He came up with the concept of dominance, where one colour was dominant over another, or recessive, meaning that two copies of a specific gene were needed in order to give the pea colouration that he wanted. He was the father of genetics as we consider it today, so much so
that we now have these conditions called Mendelian conditions, from the name Mendel. These are genetic conditions with 100% penetrance, which means that if you have a specific mutation in a given gene, you will get a specific disease. For example, cystic fibrosis is what we call an autosomal recessive condition, autosomal means that the mutation is not on a sex chromosome, and recessive means that you need two copies of a specific mutation in order to give you a disease. Giles Yeo: Cystic fibrosis is caused by mutations on an autosomal chromosome, and you need two copies of the mutation to see the disease. The next one we have here is Duchenne's Muscular Dystrophy. This is an X-linked recessive disease, which means that it's a mutation on chromosome X. And it's recessive in a sense, so you need both copies of the gene to be mutated if you are female, but as a male because you only have one X chromosome, then any mutation on the X chromosome will lead to the disease, thus it's called an X-linked recessive disorder. The final one listed here is Huntington's disease, which is an autosomal dominant mutation. The mutation happens not on the sex chromosome and you only need one mutation, because the mutation is dominant you will actually end up with the disease. So many of us will have studied this in high school and I'm sorry if this is 'teaching Grandma to suck eggs', but I thought we should begin from an even playing field so we all understand what's going on. The first question relates to how we look at DNA, so