If you know someone who never gives a treat or who rarely pays for his share of a meal, don’t blame him — blame his mean genes.

Scientists have pinpointed a stretch of DNA that makes people tight—fisted. One in four of us carries the ‘mean gene,’ inherited from parents.

Such thrifty sorts may also constantly bum off cigarettes from others, or regularly borrow cash for bus fares, but rarely pay it back, according to the journal Social Cognitive and Affective Neuroscience.

Keen to look out for themselves and their cash, they may also insist on totting up every item of food they have eaten in a restaurant, rather than simply splitting the bill equally, reports the Daily Mail.

German researchers took cell samples of over 100 persons and tested them for a gene called COMT.

The gene, which comes in ‘G’ and ‘A’ versions, is known to influence brain chemistry. The researchers believed it may do so in a way that affects how generous — or not — we are towards others.

The volunteers were given a gambling computer game to play and then told they could donate some or all of their winnings to a poor child in Peru. To tug the heart strings, they were also shown a picture of a girl called Lina and a bracelet that she had knitted.

The type of COMT gene did not affect how much the men and women won on the gambling game but it determined how much they gave to charity.

More than 20 percent of those with the ‘G’ version gave all the cash they had won to Lina, but fewer than two percent with the ‘A’ version were as generous.

On an average, those with the ‘A’ version, or the ‘mean gene’, gave less than half as much to charity, the University of Bonn study found.