Low genetic diversity leads to low IQ
Most animals, including humans, take steps to find a mating partner that is as genetically different from themselves as possible. And in our case that's with good reason, because scientists have now discovered that people who inherit the same versions of certain genes from their mum AND their dad, which is what can happen if you marry a close relative like your cousin, are likely to be shorter and do less well at school than those who get different versions from each parent. To find out more, Kat Arney spoke to University of Edinburgh researcher Peter Joshi, who was part of the study team.
Peter - What we're doing is using modern genomic techniques to measure genetic diversity. And The way that we're doing that is that we're using 350,000 people in total. To make sure that the study is very robust, we used 100 different populations across the world with all of that information and then collating it centrally in Edinburgh, we basically looked and measured the genetic diversity of each of those individuals.
Kat - So, you've got hundreds of thousands of people from populations across the world. How are you analysing their genomes? What are you looking at?
Peter - What we do is we look at the genetic diversity of individual people within that population and compare them with other people within the population. And At the same time, we look at their cognitive ability, height or blood pressure and within that population, see whether or not there's an association between genetic diversity and say, educational attainment. Having done that, we then combine all the results of the different studies to see whether or not the effect is robust and reliable across lots of populations.
Kat - So, when you started looking at the levels of diversity about whether people have two copies of gene or two different copies of a gene, what did you start to find?
Peter - We're looking at the whole of the genetic code of each individual and we're scanning along that genetic code and checking what proportion of that genetic code is identical from the mother and the father. What we typically find is that about 0.1 per cent of the genetic code is inherited identical from the mother and the father. But that number varies from individual to individual. With some people, it might be none at all and in some other people, it might be 3 or 4 times that. What we find is that if you've inherited 2 or 3, 3 or 4 times the norm in terms of lack of diversity that reduces educational attainment, cognitive ability and height.
Kat - So people who've got more similar genes from their parents, they don't do as well at school and they're shorter?
Peter - Yes, but it's also important to recognise that these effects are small. But on an individual level, it wouldn't be measurable. That's why we needed 350,000 people to robustly demonstrate that it was a real effect. The mechanism that we think might be involved is that there will be things associated with development that might underpin growth and therefore your height. And so, it's not height itself in a way that is being controlled in this way but it's the underlying biological systems and two bad copies might affect height in that way up and cognitive ability. If that happens, if these traits are favoured by evolution then we see this overall effect whereas for traits that are not subject to evolutionary pressures, we don't see that in quite the same way. It's speculation and one of the things we want to look at in the next stage of our study but it's to understand perhaps what's going on in more detail in terms of inheriting two identical copies of a defective gene.