It’s in our genes

Published 12:00 am Sunday, February 24, 2008

Maybe it’s the eyes. Maybe it’s the hair. Maybe it’s the smile.

It’s difficult to pinpoint just why the Mayo girls look so much alike, but make no mistake — the resemblance is uncanny. Six-year-old Liza has her mother Monica’s blue-green eyes. Nine-year-old Kate has her dark, auburn hair.

“I hear Kate really looks like me a lot,” Monica said. “The haircut probably helps and we dress alike sometimes.”

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Monica said she gets tons of comments about the three of them looking alike. Recently, someone mistook a painting of Kate as a painting of Monica as a child.

“A lot of relatives say the girls look like me when I was little,” she said.

The Mayos’ resemblance isn’t unusual for families. Most people would agree they share some similarities with their family members. “She’s got her daddy’s eyes,” or “He has his mother’s smile” are fairly common around the dinner table at family gatherings.

But what makes someone resemble someone else? It’s really just Biology 101.

“You get half of your DNA from your mother and half from your father,” said Trinity Episcopal Day School science teacher Anne McMullen. “But your mother got half from her father and half from her mother and your father did too. So, the question is, ‘which genes will children get?’ Siblings that look alike got the same genes.”

Obviously, Liza, Kate and Monica have similar genes. Liza and Monica’s blue-green eyes are the result of the presence of both colors, McMullen said.

“Anything between brown and blue means a little of each,” she said. “Lighter eye colors are a recessive trait and not as common.”

However, Kate and Monica’s nearly-identical dark hair is a fairly common occurrence in humans.

“If you believe human life originated in Africa, dark features must be dominant all the time,” McMullen said.

It may be Biology 101, but predicting genetic features is no easy task. As most ninth-grade biology students know, the Punnett square is science’s attempt to simplify this. The Punnett square, named after 20th century geneticist Reginald Punnett, predicts all possible gene combinations in a cross of parents. For example, if mom has brown eyes and dad has blue, the Punnett square would predict that the offspring would likely have brown eyes since brown is a dominant trait.

In Kate’s case, the Punnett square would show that at least one of her parents had dark hair. And lo and behold, the square is right — Monica and her husband Monty both have dark hair. Endless possibilities exist when analyzing genetics with a Punnet square. In theory, parents could closely predict what their child will look like, as long as they know their own genes.

“People don’t like to talk about that, because people start thinking about making everyone tall and pretty,” McMullen said. “The Nazis had it right. You can determine what people will look like.”

McMullen said most geneticists no longer use the Punnett square. They now focus on DNA molecules to predict genetic traits.

“The more DNA molecules look alike, the closer people will resemble each other,” she said.

And resembling your family members may be evolution’s attempt to help you survive, McMullen said.

“From an evolutionary perspective, resembling your parents may be a more successful form of life,” she said. “Maybe thousands of years ago, if you looked like your parents, they would be more likely to keep you around. They wouldn’t kill you or kick you out of the home.”

It all sounds fairly simple. We know how we look like our parents and maybe even why, but science doesn’t stop with these explanations.

The face is undeniably the most recognizable part of the human body. When someone says, “He looks just like his brother,” they are likely referring to similar facial features. When neighbors tell Monica that she looks like her daughters, it’s their faces they’re talking about.

But what makes a face recognizable? What makes one face resemble another face? The answer may not be as simple as Biology 101, but science has taken a stab at figuring it out.

German neuroscientist Dr. Doris Tsao believes she has the answer. After researching face recognition in monkeys, Tsao believes that certain cells in the human brain may favor faces more than other objects. According to Tsao’s research, these cells “responded to human, monkey and even highly simplified cartoon faces.”

Her research suggests that these cells recognize faces on the basis of visual shape.

“Most cells responded best to extreme features such as large irises or big faces,” Tsao wrote. “Each cell acts as a set of face-specific rulers, measuring faces along multiple distinct dimensions.”

It sounds complicated, but to put it simply — certain cells in the brain are responsible for face recognition. These cells make it possible for us to recognize our family and friends. They also make it possible for people to see that Liza and Kate look a lot like Monica.

Sure, most people could care less about how the human brain recognizes a face. But, without a doubt, most are glad that it does.