What genes can say about your baby-to-be

By Published On: August 30th, 2010

happybabyHow many of us really, truly know where babies come from? Sure, there’s the sperm-meets-egg bit we explain to curious 10-year-olds, but there’s a lot more to it than that. Each little spermatozoon and ovum contains loads of genetic instructions, and when they combine, many of baby’s future characteristics are immediately decided. Learning about the process can help us form inferences about baby’s potential (plus, it’s just plain fun!).
Know the basics

At conception, mom and dad’s chromosomes mingle to determine baby’s sex. Mom’s egg always carries an X-gender chromosome, and dad’s swimmer will contribute either a girl-generating X chromosome or a boy-making Y chromosome. In short, dad’s donation decides the gender. (So when Henry VIII was dismissing wives who wouldn’t produce heirs, he really should have blamed his own sperm cells!)
It’s a common misconception that gender is a 50/50 thing: In reality, more males than females are born each year. Why? According to the CDC’s National Vital Statistics Reports of 2005, “Male infants are more susceptible to illness and have higher infant mortality rates, including rates of Sudden Infant Death Syndrome.” So supplying more males than females initially may be nature’s way of evening the score.
Along with establishing baby’s sex, the sperm and egg contain all the other genes that will determine aspects of her appearance, personality and health. Each parent contributes 23 chromosomes which pair up for a total of 46, or 23 pairs. Every chromosome carries thousands of genes, explaining why siblings are apt to have some similarities but definite differences as well—the sum total couldn’t possibly be the same with all those potential pairings.
Imagine the future

While “What will baby look like?” websites like morphthing.com are good for giggles, merging mom and pop’s faces probably won’t give you a super accurate impression of your kid’s could-be countenance. Louis Bartoshesky, MD, MPH, a medical genetics expert with Christiana Care Health System in Newark, Delaware, states, “Dozens—and maybe hundreds—of genes from each parent are involved [in aspects of baby’s appearance]. And rather rarely, a single gene variant (sometimes called a ‘mutation’) can have a very important effect.” There’s no easy way to know precisely what a child will look like—she could seem more like mom, just like dad, or somewhere in between.
Researchers say that traits such as height, skin tone, hair color and eye color are much too complex to predict with total accuracy. Of course, a child with brown-eyed relatives on both sides is likely to inherit the same look, but a baby with multiple eye colors in her family history could end up with any one of the shades represented. Because there are multiple genes involved, a simple recessive-versus-dominant Punnett square won’t provide a solid answer. To look for inheritance clues, climb your family tree and find out which characteristics the last few generations sported. Who knows—your grandma’s emerald green peepers might just make a reappearance! Sometimes an infant’s looks seem to come out of nowhere. But when a redheaded baby is born to a family with no recorded history of carrot tops, don’t blame the milkman! According to Bartoshesky, surprise physical traits may be explained by “mutation, multiple gene interactions, a recessive trait or inaccurate reporting of great-granddad’s hair color.”
Give by science, live by example 

Here’s where the nature-versus-nurture discussion really comes into play. Some personality traits are linked to genes while others are entirely learned. Environmental factors can influence a child’s height, weight and general appearance (say yes to exercise, sleep and healthy eating, and no to secondhand smoke and a fast food diet), and they’ll have a pronounced effect upon her personality as well.
Although parents shouldn’t be held completely responsible for their kids’ angelic behavior or crusty demeanor, they do have a strong influence over their attitudes and decisions. Especially in the early years—before peers begin to play important roles—little ones are watching their parents’ every move, picking up and storing away relationship pointers, communication patterns and coping mechanisms. As if that’s not enough to make you nervous, work habits and overall outlook on life are commonly passed down by example as well.
Assess the risks

“There are hundreds of disorders related to changes in a single gene or pair of genes, but each of these is rare,” says Bartoshesky. If you know your family has a history of hereditary disease, you belong to an ethnic group with increased risks, or you’re over age 35, it’s especially prudent to seek genetic counseling before conception.
“Genetic counselors are specially trained in both medical genetics and counseling,” says Elizabeth Kearney, MS, CGC, President of the National Society of Genetic Counselors. “Sometimes, family history is sufficient to determine whether there is a higher chance for a baby to develop an inherited condition. Other times, a genetic counselor may offer a genetic test to a couple based on their … background.”
If the parents are determined to be at risk of producing a child with a genetic disease, they then have the choice of pursuing in vitro fertilization with genetic testing of the embryos, which can give them control over whether or not a fatal disease is passed on. Other management options may also be available. For example, “someone who has a close relative with spina bifida … may want to talk with her doctor about taking higher levels of certain vitamins prior to pregnancy,” suggests Kearney.
To find a genetic counselor, visit the National Society of Genetic Counselors at nsgc.org. Your local counselor’s staff may be able to help you determine how much applicable coverage your insurance company will supply.
It’s easy to worry about what might possibly go wrong, but try to stay positive about your pregnancy. Maintaining low stress levels is better for baby, and odds are she’ll arrive strong and healthy with a bright future ahead of her. She’ll be a lovely little combination of your genes and your partner’s—when you think about it, that’s pretty darn cool!