THE DNA profile of your husband or wife is influencing everything from how often you eat beef or oily fish to how much time you spend watching television, according to a new study.

Researchers at Edinburgh University also found that the female partner’s genes in a couple will hold more sway over her partner’s behaviour than the other way round.

The findings, published in the journal Nature Human Behaviour, are based on a phenomenon known as indirect genetic effects (IGEs).

This is when the genotype - or genetic profile - of one person affects the observable characteristics of another individual with whom they share an environment.

Evidence of IGEs have previously been demonstrated for so-called vertical relationships, such as those between a parent and their child.

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For example, a mother’s genes can affect her baby’s birthweight and parents’ genetic make-up has been linked their offspring’s cognitive ability and educational attainment, even though these are not directly inheritable traits.

There has been less research on ‘horizontal’ IGEs, such as those between long-term romantic couples, but some studies have previously found evidence of the pattern with groups of school friends in relation to educational attainment.

Professor Albert Tenesa, the lead author of the study and chair of quantitative genetics at the Roslin Institute, said the phenomenon was underpinned by how people’s own genetic predispositions - such as concentration - affect their behaviour, and in turn the risks or benefits that those around them would experience as a result.

He said: “I might not smoke, but if all my family around me are smokers and that part of their smoking behaviour is determined by genes, 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 children behave well, they’re relatively clever, then the chances are the someone has a good environment to make their genes perform better, thereby affecting the educational attainment of the group.

“It’s been shown in animals too. If you put a very aggressive animal in a pen, that changes the whole dynamics of the behaviour of the rest.

"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 also in humans.

“If someone is depressed at home, that will change the whole dynamics.”

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Prof Tenesa and colleagues sought out to determine how much one person’s genotype can affect the traits and behaviours of their partner.

They analysed DNA samples from 80,889 heterosexual couples of European ancestry stored at the UK biobank, and compared these against self-completed health and lifestyle questionnaires covering everything from diet and mood swings, to how many hours they slept each night and smoking habits.

This enabled the scientists to gather data in relation to 105 complex traits.

On average they found that one partner’s genotype explained 1.5% of the variance among 51 observable traits, although this was higher for certain characteristics such as mental health, dietary traits and educational attainment.

Of these 51, they found “consistent evidence” of a link for 13 traits: body fat percentage, ease of skin tanning, dried fruit intake, oily fish intake frequency, beef intake frequency, lamb/mutton intake frequency, time spent watching television, smoking status, number of siblings, self-reported astigmatism, educational attainment, mood swings and fed-up feelings.

They note that they the “female to male effect was significantly larger than male to female” for six traits mainly related to diet and obesity, such as cereal intake, beef intake frequency, or waist-to-hip ratio.

The researchers added that the “biggest challenge” is to disentangle how much traits within a couple are caused specifically by genes, and how much they are due to “assortative mating” - in other words, that like attracts like.

“There is a tendency for people to choose someone who is more alike to them,” said Prof Tenesa.

“The challenge of this paper is to explain whether the genetics - on top of that effect - explain more than you would expect, and we showed that it did.

“We showed that this effect couldn’t just be explained by assortative mating - something else is going on.

“A lot of them are related to food intake, which means that if one half of the couple likes something the other member of the couple is more likely to eat that.

"That makes sense because in families food tends to be shared. So whoever is in charge of preparing the food determines quite a lot of what the rest of the family eat.

“We have shown in the past that there are genetic predispositions to whether you like meat or fish or vegetables and so on.

"To some extent that then forms part of the environment of someone else.”

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Prof Tenesa added: “I think the most important thing to take from this study is that what we call the environmental risk factors, like smoking, part of them are determined by others. We really knew very little about that.

“We just assumed that it was a personal choice. And while some of it is a personal choice, some of it is really not, and I find that quite interesting.

“Another thing is that the environmental and the risk factors are very difficult to measure, but the genotypes are something we can measure very accurately from birth. They don’t change.

“There will be a point when we know each part of the genome and what behaviour they affect, so that could actually be a more consistent way of measuring the environment of others.”