Border and his colleagues are not the first to raise the possibility of a false genetic correlation. When designing studies, geneticists can control for the effects of factors such as parental characteristics and childhood environment by comparing people who have those things in common—i.e. siblings sister. Earlier this year, statistical geneticist Laurence Howe and a team of researchers did just that. When Howe compared siblings, he observed There was no genetic correlation between BMI and years of schooling. Somehow, it was the parents, not the genes themselves, that made weight and education seem to be genetically linked.
But Howe’s research doesn’t exactly explain how Parents play a role. There are some promising possibilities. Not only do parents pass on genes to their children, but they also pass on their socioeconomic status, which has consequences for both schooling and diet. And, of course, parents often choose who they breed with. Loic Yengo, team leader of the Statistical Genomics Laboratory at the University of Queensland, says that geneticists have realized that interbreeding between traits could—in theory—inflate genetic correlations. transmission. But no one has yet given concrete evidence that it did.
Border and his colleagues found that evidence. Detailed study of crossbreeding between traits requires knowing the extent to which it actually occurs in the real world. It seems reasonable that depressed people might marry anxious people because they have shared experiences of living with mental illness, or that educated people would be more likely to marry people who score well on tests. IQ test, but Border needs to put the numbers on those trends. The team was able to find the information they needed in the UK Biobank, a huge dataset that includes genetic, medical and demographic data on hundreds of thousands of UK residents. They found that the more likely people with a certain pair of traits were to pair up, the more likely those traits were to be genetically correlated. It is therefore reasonable to suspect that mixed mating is in fact making some genetic correlations appear stronger than they would otherwise be.
However, this observation does not demonstrate that mixed mating can produce the illusion of a nonexistent genetic link. So Border and his team turned to a computational approach: Following marital trends they had observed in real-world Biobank data, they simulated a group of people mating into couples. . These imaginary couples reproduce, and their children find a mate, and their children’s offspring—etc. Scientists tracked the genes and characteristics of all these clones, and using that information, they were able to calculate genetic correlations across generations. What they found confirmed their suspicions – even if the two traits were completely unrelated in the first generation, if people with those traits tend to interbreed, then Eventually the genes started to seem to correlate with each other. Based on the simulations, they estimated that random mating alone could explain half of the genetic correlation between BMI and education level.
But the mixed mating didn’t go so far as to explain some of the other obvious correlations they simulated. It seems to play a smaller role in the genetic correlation between some pairs of mental conditions, like bipolar disorder and schizophrenia, or major depression and anxiety. Because each pair of conditions shares so many genetic similarities, some scientists have wondered whether they should be treated as separate conditions. Even taking into account mixed mating, that argument seems to hold its ground.
