In the second post in our mini-series leading up to my talk with Emma Beswick for Your Life and Cancer 2020 we look at how our genes differ from each other.
In fact they don’t! We all have the same gene set containing around 20000 genes and we all have the same genes in the same place (locus) on the same chromosomes, though boys have a bit missing.
Differences between people occur when they have another variant of the same gene.
For example, there is a gene for hair colour and some people have the red version and some have the brown version. Same gene, different variant.
These variants are called alleles.
So while we all have a gene for hair colour I’ve got the dark brown shiny allele and you might have the light blonde frizzy allele. We could debate all day which one of those is the better gene and not get very far. But some alleles are definitely associated with longer life and better health than others which is one of the reasons they’re so interesting to study.
We normally have 2 alleles for every gene – one from mum and one from dad (inherited from their mum and dad, and so on). Sometimes mum’s genes win (and get expressed) and sometimes dad’s do. We think of that as dominant/recessive characteristics. Dominant genes tend to be more common in populations and tend to result in typical racial characteristics or health outcomes; they often confer a survival advantage. Sometimes diseases are caused when we inherit two recessive genes – cystic fibrosis for example – which is why genetic counselling pre-conception is on the increase.
Most characteristics, eye colour included, are controlled by a set of genes, not just one. That gives a much wider variety of options and explains why we don’t actually have just blue, green and brown eyes. Everyone’s eyes are different because a number of genes are involved in creating the colour.
When the two sides of our gene inheritance come together in a typical way, similar to most of the population, we tend to call it a ‘wild type’ gene. Non-standard expression is normally called a mutation – which may or may not be a good thing. Most surviving mutations confer some sort of survival advantage. We’ve learned a lot about genetics over the years by studying gene mutations.
The picture is of my identical twin sisters who get easier to distinguish year as the effect of different diet and lifestyle experiences play out in their lives.