The complex gene pool you hand down can shape everything -- from how funny your child is to whether he likes peas.
The instant our children are born, we look for reflections of ourselves in them. When Evie Crosby, of Tallahassee, Florida, delivered her son, Wyatt, she immediately asked her husband, Adam, "Does he have your chin?" Adam gave her a thumbs-up as the nurses cooed over Wyatt's deep cleft -- just as nurses had done when Adam was born 30 years earlier. Moments like these are more than a little profound. Seeing yourself -- and your spouse -- in your baby makes you truly feel like a family. Inheritance goes far beyond eye and hair color: Genes can even shape personality traits like leadership and spirituality. Despite startling advances in genetics, our understanding of how genes and environment interact is far from perfect. "Many traits have a large hereditary component, but genetics isn't destiny -- genes are just one influence on how kids turn out," says Joann Bodurtha, MD, professor of human genetics at Virginia Commonwealth University, in Richmond.
It's easiest to spot similarities in your child's appearance. "Our 2-1/2-year-old daughter, Amber, is really a mix of both families," says Rose McKinney, of Oshawa, Ontario. "She has my face and my grandmother's stick-straight hair, but her dad's brown eyes and long, big toes." Amber's eye color isn't surprising: Brown eyes are considered a dominant trait, so if one parent has the gene for brown and the other has a recessive gene for blue, brown usually wins. Even so, nobody can predict eye pigment for sure: In some cases, both parents have blue eyes but still have a brown-eyed baby, which shouldn't happen if the trait followed the simple dominant-recessive rule.
"Most traits are actually determined by many genes working together, rather than a single gene," says Kate Garber, PhD, director of education in the department of human genetics at Emory University School of Medicine, in Atlanta. Take hair color, for example. If a father carries only a dominant gene for brown hair and the mother carries only a recessive gene for blond, their children should all have brown hair, but some of their grandchildren are likely to be blond. Reason: The kids inherit both sets of genes, which can combine with blond genes from their mates to produce fair-haired offspring. But don't blame the mailman if your child's hair is surprisingly red -- the interplay of genes can create all sorts of unexpected traits. And if your son eventually loses his hair, he can point a finger at either parent: Contrary to popular belief, the dominant gene for male-pattern baldness can be passed down by moms or dads.
Joseph Chisolm, of Secaucus, New Jersey, certainly knows how arbitrary inheritance can be. He's black and his wife, Donelle, is white, so they weren't surprised that their first child, 4-year-old Jaydon, was dark-skinned and brown-eyed. "He could pass for Hispanic," Chisolm says. But their 1-year-old son, Jordon, is startlingly different: "He's white, blond, and blue-eyed," says Chisolm. "You would never guess that he was the child of a mixed-race couple."
Even when your kids don't look exactly like you, there may still be subtle but striking resemblances. One study found that families tend to have similar facial expressions when they're happy, sad, angry, disgusted, surprised, or thinking hard. And kids don't just pick up these reactions from watching us: Blind members of 21 families in the study also grimaced, smiled, and scowled like their relatives 80 percent of the time. Other likenesses are quirkier. Both Kim Whorton, of Birmingham, Alabama, and her daughter Zoe, the oldest of 3-year-old triplets, have dimples in their shoulder blades -- a rare trait that's been traced to an abnormality on a specific chromosome.
In some cases, one genetic trait may be linked to others. Check the hair whorl at the top of your child's head: If it swirls counterclockwise, he has a 50-50 chance of being left-handed or ambidextrous, which suggests that both hair pattern and handedness are driven by some of the same genes.
Scientists have little doubt that genes can affect a child's behavior, but exactly how nature and nurture work together is still somewhat of a mystery. One recent study concluded that almost all psychological traits are at least somewhat genetic. Research has also shown that twins often have similar personalities even when they have been raised apart. "When parents say, 'My child has my hot temper,' there is definitely an element of truth to that," says Greg Carey, PhD, associate professor at the Institute for Behavioral Genetics at the University of Colorado, Boulder.
The resemblances can be uncanny. Amber Carlsen, of Salt Lake City, says her 2-year-old daughter, Haylee, is a deja vu version of herself as a child -- bossy, independent, and fastidious. "I'll ask my mother to watch Haylee in the tub for a minute and then come back to find Mom laughing," says Carlsen. "She'll say, 'Haylee's so much like you were, it's just amazing.'" One day, Haylee came home from the babysitter's house all excited about Strawberry Shortcake characters -- and she's been a huge fan ever since. "It stopped me dead in my tracks because I loved those pink dolls when I was a kid but have never introduced them to Haylee," says Carlsen.
"There's no Strawberry Shortcake gene," says Dr. Carey, "but genetics can certainly shape preferences for things like color, which could lead a child to make choices that are similar to a parent's." Even favorite foods may be partly rooted in biology. One recent study found that kids who have a taste gene that's associated with a sensitivity to bitterness are less likely to pick milk or water as their favorite drink and more likely to love sugary soft drinks and cereals.
However, there's almost always a connection between genetics and environment. Musical talent is a classic example. People who have perfect pitch are four times more likely than those with only average singing voices to say that a relative has this natural gift. Yet research has also found that most people with perfect pitch started taking music lessons before age 6, and that only 3 percent of people who started voice lessons after age 9 have perfect pitch -- suggesting that both genetics and training affect one's singing voice. "It's simplistic to say that artistic and intelligence traits are determined by genetics, because even a gifted child needs the right environment to thrive," says Dr. Garber. Average IQ scores have gone up in the past 50 years thanks to changes such as better early-childhood education, experts say, not because we're innately smarter. And intelligence may run in families partly because bright parents tend to provide a richer learning environment -- by having more books, for example. In fact, two recent studies found that the IQ of firstborn children is slightly higher than that of their younger siblings -- possibly because they received more undivided attention.
"Almost all talents need to be practiced," says Dr. Carey. "Even if you're genetically predisposed to be a great basketball player, you still need to shoot a lot of free throws." The environment a child grows up in can also affect other genetic traits. "The impact of genes for height can be modified by the foods you eat," says Dr. Bodurtha. "And environment is enormously important during development and early childhood. For example, your child could have genetic potential for a high IQ, but if you drank alcohol during pregnancy, it may be lower."
Sometimes, our children pick up traits we don't intend to teach -- just by living with us. Nora Flanagan's 1-year-old son, Kevin, was adopted but has definitely taken on some family traits. "My two brothers and I have the same up-to-something smirk, and Kevin's got it down to the last detail," says Flanagan, of Chicago. He also has a boisterous laugh that leaves him out of breath, just like both of his adoptive parents. "We keep in touch with Kevin's birth mother, who is more reserved, and it's been eye-opening to see how he's a combination of all of us," says Flanagan.
Predicting Health Problems
We all know that having a family history of an illness can put a child at risk. Some diseases, such as cystic fibrosis and hemophilia, are directly caused by an abnormality on just one gene. "Children who inherit a defect in the gene for cystic fibrosis from both parents, for example, will almost certainly get the disease," says Dr. Garber. However, most conditions involve multiple genes and complex traits that may increase a child's risk but not automatically doom him to developing the disease down the road. Type 2 diabetes is strongly genetic: If you have it before age 50, your child has a one-in-seven chance of developing it as well. However, people in non-Western countries who eat better don't get diabetes as often, which shows that lifestyle can reduce the risk. Similarly, genetics account for an estimated 75 to 80 percent of the difference between a skinny kid and an obese one, but even if a child has "fat genes," he can avoid weight-related problems like heart disease if he has healthy habits.
"Being aware of the risk can steer you and your child to healthier choices all her life," says Dr. Garber. For example, if your father had skin cancer and your child has strawberry-blond hair, you should be extra vigilant about using sunscreen. Parents with a history of depression can be on the lookout for symptoms in their kids and get them help as soon as possible -- if the condition ever occurs.
And that's a big if. "The more we know about the interplay of genetics and environment, the more we realize that human health and behavior are too complicated to be caused by just one thing," says Dr. Carey. "Our kids are like us in some ways but not in all. Whenever parents say, 'My child is just like me,' they usually qualify it by saying 'except for....'"
Scientists used to think people had up to 100,000 genes -- until the Human Genome Project revealed that we actually have closer to 25,000. Why the huge overestimate? It turns out most genes are multitaskers and do their jobs by marshalling other genes -- turning them on and off or boosting their effects -- so we need fewer genes overall. As a result, few characteristics can actually be traced back to a single gene (there aren't enough genes to go around for that). Nevertheless, kids have a greater chance of inheriting some characteristics rather than others. Here are some of the traits you're most likely to pass on.
- Body fat
- Fingerprint ridge count
- Epilepsy (some forms)
- Cystic fibrosis
- Type 2 diabetes
- Blood pressure
- Maximum heart rate
- Cleft lip/palate
- Diet preferences
- Type 1 diabetes
Copyright © 2007. Used with permission from the September 2007 issue of Parents magazine.
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