THE DNA profile of your husband or wife affects everything from how often you eat beef or fatty fish to how much time you spend watching TV, a new study suggests.
Researchers at the University of Edinburgh also found that the genes of the female partner in a couple have more influence on her partner’s behavior than the other way around.
The findings, published in the journal Nature Human Behavior, are based on a phenomenon known as indirect genetic effects (IGEs) (IGEs).
This means that one person’s genotype – or genetic profile – affects the observable characteristics of another person with whom they share an environment.
Evidence for IGEs has already been provided for so-called vertical relationships, such as that between a parent and his or her child.
For example, a mother’s genes can influence her child’s birth weight, and a parent’s genetic makeup has been linked to the cognitive abilities and educational attainment of her offspring, although these are not directly heritable traits.
Less research has been done on “horizontal” IGEs, such as between long-term lovers, but some studies have already found evidence of the pattern among groups of school friends in relation to educational attainment.
Professor Albert Tenesa, lead author of the study and chair of quantitative genetics at the Roslin Institute, said the phenomenon is underpinned by how people’s own genetic predispositions – such as concentration – influence their behavior, and therefore the risks or benefits people around them would experience as a result.
He said, “I may not smoke, but if everyone in my family around me is a smoker and part of their smoking behavior is determined by genes, then those genes affect how much smoke there is in the household, and that affects my risk of lung cancer.
“Also, if your class is a good class where the kids are well-behaved and relatively smart, then there’s a good chance that someone has a good environment where their genes perform better, which affects the educational level of the group.
“This has also been shown in animals. If you put a very aggressive animal in an enclosure, it changes the whole dynamics of the behavior of the others. That aggressiveness is partly due to the animal’s genes, but that affects who eats first, how they behave, how they communicate with each other, and that happens in humans, too.
“If someone is depressed at home, that changes the whole dynamic.”
Prof. Tenesa and colleagues wanted to find out how much a person’s genotype can influence their partner’s traits and behaviors.
They analyzed DNA samples from 80,889 heterosexual couples of European descent stored in the U.K. Biobank and compared them to self-completed health and lifestyle questionnaires that covered everything from diet and mood swings to the number of hours they slept each night and smoking habits.
In this way, the researchers were able to collect data related to 105 complex characteristics.
On average, they found that a partner’s genotype explained 1.5 percent of the variance in 51 observable traits, although this value was higher for certain traits such as mental health, dietary habits, and education level.
Of these 51 traits, they found “consistent evidence” of association for 13 traits: Body fat percentage, ease of skin tanning, consumption of dried fruit, frequency of eating oily fish, frequency of eating beef, lamb/lamb meat, time spent watching TV, smoking status, number of siblings, self-reported astigmatism, education level, mood swings, and being annoyed.
They note that the “female-to-male effect was significantly larger than the male-to-female effect” for six characteristics mainly related to diet and obesity, such as grain consumption, frequency of beef consumption, or waist-to-hip ratio.
The researchers added that the “biggest challenge” is distinguishing how much of the traits within a pair are specifically caused by genes and how much is due to “assortative mating” – in other words, that like attracts like.
“There is a tendency for people to choose someone who is more like them,” Prof. Tenesa says.
“The challenge of this work is to explain whether genetics – in addition to this effect – explains more than one would expect, and we have shown that it does.
“We have shown