Maybe you have Liz Taylor lavender eyes that still melt hearts. Or maybe you have a Cyrano nose you wouldn’t wish on your worst enemy. What are the odds your grandchildren will be blessed — or saddled — with your most distinguishing features?
Why one child resembles his maternal grandfather while another favors her paternal grandmother involves a staggering set of variables, says University of Michigan genetics professor David Burke.
“Think about the probability of drawing four aces in a hand of poker — and that’s just 52 cards,” Burke says. “We’re talking here about 100,000 genes that get reshuffled with every generation in a complicated process that, truth be told, we really still don’t understand.”
New genetic testing techniques can now reveal individuals’ shared lineage going back multiple generations but still can’t determine if your grandchild will have your high cheek bones. And yet there is some familial resemblance in every new grandchild.
The features you’re more likely to see carried over in your new grandchild are more likely to include hair, skin, and eye color, than the actual contours of your face, says Barry Starr, director of Stanford at The Tech, a program run by the Stanford University genetics department at the Tech Museum of Innovation in San Jose, Calif.
While determining a baby’s eye color is a function of dominant and recessive genes, Starr says, skin and hair color are generally a result of blending. For example, a child whose mother is a blonde and father is a brunette stands a good chance of having sandy blonde hair — but there are no guarantees.
There are certain physical characteristics, or “single-gene traits,” that are determined by the presence of one specific gene, but they’re relatively few — think red hair, dimples, a widow’s peak, or the ability to roll one’s tongue. The red-hair gene usually carries with it the likelihood of freckles and pale skin — both of which can also surface through various gene combinations.
Not by genes alone
Anne Matthews, director of the graduate program in genetic counseling at Case Western University in Cleveland, likens the process of passing down facial traits to baking a cake. And genes aren’t the only ingredients. In the “oven” — a mother’s womb — a wide variety of non-genetic environmental factors can have a potentially major effect on a fetus that scientists are still trying to understand.
“Every time you bake a cake, even if you think you put in exactly the same measure of ingredients and cooked it at the exact same temperature as before, it never comes out exactly the same way,” Matthews says. “The shape of a nose alone, for instance, has to do with hundreds of genes all working in concert.”
Eyes of the beholder
If there are so few traits that carry directly from one generation to the next, and if general appearance is determined by such a wide range of genetic and environmental factors, then why does one grandparent look at a newborn and see herself in his eyes, while another looks at the same grandchild and sees his own mouth smiling back at him? More than anything, it’s all in the eye of the beholder, says Angela Trepanier, president of the National Society of Genetic Counselors.
“I might be more inclined to look at a child’s eyes while someone else might focus on the nose and cheekbones,” she says. “Why we have those specific recognition patterns, we have no idea — but there’s probably some genetic basis to that too.”
Parents often speak of seeing a grandparent’s personality reflected in a child’s mannerisms or facial expressions, and Matthews agrees there’s something to that: “How a child smiles affects their looks and who they might more likely resemble.”
The search continues
Geneticists are making remarkable discoveries since the mapping of the human genome, but their work, probably correctly, remains concentrated on using the genome for medical applications, rather than to answer question like whom a child will most resemble. For example, scientists have studied the red-hair gene somewhat more closely than others because redheads are more inclined to get skin cancer due to their fair skin.
“We’re still looking for what might give you an aortic aneurism because that’s what gets funded,” Burke says, “not why you look like Uncle Bob.”
The experts say that any future discoveries about how appearance is carried through a child’s genes are likely to come as a byproduct of other research, such as DNA sampling for crime-scene investigations.
Until then, Trepanier says, predicting whom a child will resemble remains open for speculation and the best science can tell you is, “It really is the luck of the draw who you end up looking like.”