HOW GENES AFFECT LOOKS
How our genes dictate our appearance
Children typically look like one or both parents. No news there. In fact, when they don’t, that’s when there’s gossip.
And there’s surely no gossip over Donald and Kiefer Sutherland, Tom and Colin Hanks, or Will and Jaden Smith, to name three of a billion examples.
Science, however, has yet to explain why Ava Phillippe looks exactly like her mother, Reese Witherspoon; or how Mamie Gummer could pass as a young version of her mom, Meryl Streep; or how genetics turned Sophie von Haselberg intothe spitting image of her mother, Bette Midler.
So finally arrives a study published Feb. 19 in Nature Genetics involving the University of Pittsburgh that takes important steps in explaining such genetics — how something so obvious involves such a complicated interaction of genes. Some of the genes responsible for facial appearance also play a role in body size, body composition including waist-to-hip ratio, and height.
“The study highlights techniques that will have future benefits in health care and associated professions, explaining the biological basis of facial shape that can be used to improve medical diagnosis and treatments,” said Stephen Richmond of Cardiff University in Wales, who wasn’t involved in the study. “Also understanding which genes affect faces and body shape will be useful in forensic science and medicine in general.”
The study reveals that many interacting genes are responsible for the nose you despise, the eyebrows that embarrass you, and the lips that you think are way too thin. And other interacting genes, in fact, led to those chipmunk cheeks, even if single genes account for less notable areas around the perimeter of the face.
When you look in the mirror, you can only blame your genes and their variants.
In all, the study that also involved researchers from Penn State and Stanford universities, with KU Leuven research university in Belgium leading the way, identified 15 genes that play an important role in facial structure.
Still, the process “is more complex than previously thought,” said Seth Weinberg, the study’s senior author, who directs the Pitt School of Dental Medicine’s CCDG 3D Facial Imaging and Morphometrics Lab. “We are attempting to map genes that underlie normal or typical variation in facial features — the kinds of variations that give each of us our unique facial appearance. But there are thousands of genes involved in facial development.”
Lead author Peter Claes of KU Leuven created a unique
computer model to analyze thousands of common points from 3-D facial images of more than 2,300 individuals. The interdisciplinary study also required researchers with different skill sets to analyze how clusters of points from that analysis came to represent distinct facial “modules.”
“Points in the same module tend to behave the same way, meaning that they vary in a coordinated fashion,” with each module representing “a distinct chunk of facial anatomy,” said Mr. Weinberg, who holds a doctorate in anthropology.
Further analysis linked each module to a specific gene or variant of that gene. That meant that each person with a specific variant showed similar facial characteristics in that part of the face.
The nose, for example, includes several modules. One gene determines the tip and another, the nostrils, with several others dictating the structure of the rest of the nose. One variation in the tip of the nose, slightly or dramatically, can alter the shape of the nostrils or bridge of the nose, revealing how modules interact. As it turns out, the face emerges as a patchwork of overlapping, interacting modules.
Or, as Mr. Weinberg explained, “Each of the 15 [genetic] signals showed unique effects of the face with each implicating different sets of modules.”
One gene — TBX15 — is involved with both the forehead and roundness of the cheek region. Mutations of that gene cause Cousin syndrome, characterized by a large protruding forehead.
Overall, the study provided “nearly complete coverage of all facial shape variation at five different levels of detail,” while advancing the field of facial genetics on several fronts, “including areas of the face whose shape involves a specific gene and variants of that gene.”
It also suggests that the timing of gene expression in the embryo determines facial characteristics and someday could be used to alter mutated genes to avoid facial birth defects.
The forensic use of DNA to describe a crime suspect isn’t yet possible and may never be, even if that idea draws the most attention in this field of study, Mr. Weinberg said.
In time, however, such studies could explore the genetic variations in different races and ethnic groups.