One of the hallmarks of medical genetics is non-directive counselling. Therefore, I was dismayed to read the case for selective paternalism in genetic testing in Wired’s Neuron Culture. In most cases, genetic tests only provide information and patients need to determine if they want the information and/or what to do with it. Genetic counsellors should help patients understand the impacts of the information.

There are lots of new terms at the start of medical school but two terms – penetrance and expressivity – seem to cause undue stress and confusion. One of the first areas of learning for the students is genetics, hopefully because it is central to understanding everything. Is the confusion due to being overwhelmed, strange associations or …?

I think it is easy to tell the terms apart – is this expert bias?

I’m sure there are fancy ways to describe penetrance and expressivity but my simple explanations:

Expressivity - how does a disease (or trait) show up?

Famous DNA double helix

We see the DNA helix everywhere. It helps market computers, trucks, and cosmetics. People use the helix as an explanation (‘in my DNA’). But do people understand this famous molecule?

In different classrooms, I have asked, “If I left DNA from a wolf in a test tube alone in a classroom, what would you do?” Some students respond, ‘drink it, so I can get wolf power’. Other students have said, ‘enter the room carefully in case the wolf is angry’. But in reality, we would just come back to DNA.

DNA is not magical. I think it is awesome but it is just a molecule. So what is it?

I love analogies and use them often to get people to think about scientific concepts in new ways. I’ll share some of my favourite ones on the blog but today, I want to talk about

(c) Hybrid Medical Animation

Well, it has happened again. Someone has confused the concept of heritability. A recent Slate article discusses the difficulties of twin studies but screws up the concept of heritability in the first paragraph, saying that genes determine 50% of the likelihood that you will vote among other things. I’ll leave others to critique the rest of the paper and I’ll focus on trying to explain heritability.

Heritability is a measure of how much variation of a trait within a population is due to genes compared to variation due to environment. It is a POPULATION measure of variation and not a simple breakdown of determinism. It is a difficult concept so perhaps some details and examples will help.

(c) Hybrid Medical Animation

I’ve been writing up my talks and am surprised how long it has taken me to get through the first part of chromosomes. I promise to move on to some more interesting things – or at least change topics – soon. For now, I thought I’d address some common questions:

• what is a chromosome vs. a sister chromatid?
• what n value do you use? (especially during meiosis)