It's in the Genes. DNA plays a role in everything from your child's silly sense of humor to her erratic sleep patterns. Find out which behaviors you passed along to your little buddy.

baby eating crayon
Credit: Buff Strickland

For weeks after my daughter Ella was born, friends and family members would play the same game: Name That Facial Feature. "Oh, she definitely has your eyes," they would announce, or "That's a Warnick chin." Once our loved ones got through with her, every inch of Ella had been assigned a pedigree on the family tree. Frankly, I couldn't see it. Ella looked like... well, herself.

When I considered her personality, however, I knew exactly whom to credit. Ellas goofy sense of humor was just like her irreverent dad's; her meltdowns when I handed her off to friends seemed like a legacy of my own introverted ways.

I've since learned that Ella's inheritances aren't as clear-cut as I'd thought: It's tricky to determine which traits are genetically hardwired and which develop from parenting habits. "The question of nature versus nurture is one for the ages," says Nathan Fox, Ph.D., director of the Child Development Lab at the University of Maryland, in College Park. There are hundreds of thousands of genes in the chromosomes we pass on to our children, with a multitude of possible combinations."It's not a simple one-to-one."

We bet you're 100 percent hooked on your baby no matter whom he takes after, but here's the scoop on which traits your tot can thank you and his daddy for.

Your baby's facial expressions

Around her daughter's first birthday, RaeAnn Ulane noticed that whenever Maddie was concentrating, she tilted her head to her side and stuck her tongue out of her mouth. "That is a father's-side-of-the-family characteristic, without a doubt," says the New Castle, Colorado, mom. "Maddie, Daddy, and Grandpa all do it. We call it the Ulane Tongue Trait."

Surprisingly, studies have found that family members often use the same quirky facial expressions to convey emotions such as anger, sadness, and yes, deep focus -- and that those signature looks usually appear by the time a baby is 6 months old. It's not only a matter of your kid playing copycat: In a recent Israeli study, researchers found that even people who were born blind made facial expressions closely resembling those of their family members. So the squinty eyes and pursed lips your baby gets when she has a bite of green beans? Take a good, long look in the mirror before you laugh.

Your baby's sleep patterns

You wished on every star that you'd give birth to a champion sleeper, but your little guy probably had his own tendencies from the get-go. Sleep needs may run in the family, according to a study in the journal Science. If your favorite hobby is napping on the couch, you could luck out with a baby who loves to snooze as much as you do (although he may require your help getting on a healthy sleep schedule). But watch out: Insomnia and stress-related tossing and turning are also genetically linked. If you struggle to doze, your mini- me might be similarly wired for more wide-awake time.

One mother even suspects that her child inherited her favorite shut-eye position. Rachel Renshaw was regaling her husband with how adorable their son, Jace, looked when sleeping with his hands neatly clasped behind his head -- until her husband burst out laughing. "Jeremy told me that I lie the exact same way Jace does when I'm in a deep sleep," says the Charlotte, North Carolina, mom.

Your baby's way of handling stress

Everyone gets a smidgeon freaked out about pregnancy, but if your anxieties are on overload, you stand a good chance of having a baby who's as nerve-addled as you are. Studies have shown that the more on edge Mom is, the more negatively baby reacts to trying situations. Experiencing lots of stress in pregnancy (the kind that comes from moving or fighting with your partner) can make it harder for baby to relax, even if you're generally laid-back. Researchers suspect that Mom's stress hormones actually affect her fetus's central nervous system.

Rather than taking a swig of guilt juice for passing along your knack for worrying, focus on the good news: Nature isn't destiny. Even a kid born with a gene that makes it hard for him to settle down can ditch the anxiety by age 1 if he has a responsive mother early on, says Cathi Propper, Ph.D., a research scientist at the University of North Carolina's Center for Developmental Science, in Chapel Hill. Bottom line: Keep calm and carry on.

Your baby's silly sense of humor

You crack up watching videos of lunatic cats on YouTube and, funny, so does your baby. So did she get her sense of humor from you? To a point. A quick-to-laugh disposition can be part of your baby's natural temperament, the bundle of personality traits that are, at least in part, genetically inherited. (Your child's mood, attention span, and activity level are also aspects of her temperament.) Where babies come by most of these characteristics isn't entirely clear. "Both genetic and environmental factors can influence temperament," says Brian D'Onofrio, Ph.D., an assistant professor in the department of psychological and brain sciences at Indiana University in Bloomington. And when you notice your kid's temperament is similar to your hubby's or your own, it's safe to assume that he either got some of your hand-me-downs or picked up aspects of your personality living under the same roof.

Still, humor is for the most part social, something your baby figures out by watching you. "When moms and dads do absurd things, like blowing raspberries or speaking in a silly voice, babies don't know what to make of it, but their parents tell them how to respond by smiling and laughing," explains Gina Mireault, Ph.D., a professor of psychology at Johnson State College, in Johnson, Vermont, who studies humor in babies. When you snicker, be it at your stinky dog or your baby's goofball faces, your munchkin is likely to start laughing too. As she gets older, she'll develop her own ideas about what's funny. Still, she'll probably always think that cracking you up is killer, meaning that she'll naturally gravitate toward whatever makes you chuckle -- even online cats.

In the end, what matters isn't deciphering your kid's intricate DNA code. Says Dr. D'Onofrio, "Better to ask yourself, 'Given my child's temperament, her own difficulties and strengths, what can I do best to parent her?'" If you let your answer guide how you mother, nature and nurture can work together -- no matter whom your child resembles.

Originally published in the December 2010 issue of American Baby magazine.

American Baby