More than you may think.

People tend to choose spouses who have similar DNA, according to scientists who reported on Monday the results of a study exploring the genetic resemblance of married couples.

The researchers examined the genetic blueprints of 825 married couples in the United States and found a significant preference for a spouse with DNA similarities across the entire human genome.

The study compared this affinity for husbands or wives with similar DNA makeup to the well-established and strong tendency of people to marry mates with similar educational levels. The researchers found that the preference for a genetically similar spouse was about a third as strong as the preference for a spouse with comparable education.

The 1,650 people studied in the research were non-Hispanic, white men and women born between the 1930s and 1950s who were taking part in a broader US government-funded study involving health and retirement.

"We do know in some sense that people prefer genetically similar spouses because we know that people tend to date and marry within their own racial and ethnic groups. We worked really hard in this study to not just replicate that fact," says researcher Benjamin Domingue of the University of Colorado's Institute of Behavioral Science, who led the study.