Genetic Variation Is the Spice of Life
The other day (you know, just during the normal flow of conversation) my mom informed me that her saliva is highly unusual. Back in college, she reminisced, she did this experiment that involved spitting into a tube then testing (using a chemical color change) to see if her spit could turn starch into sugar. Normal spit can: It contains an enzyme (amylase) that begins the digestion of starch way up in our mouths. “But as there wasn’t any in my spit,” said my mom, “it never turned anything any color whatsoever.”
Wow! Could it be that my mother is an unusual genetic variant? Could this be a trait that runs in our family? To find out if such folks are known to science, I checked with a veritable treasure trove of such variations--put together by a pioneer in human genetics research, Dr. Victor McKusick. The database, known as the Online Mendelian Inheritance in Man (https://www.ncbi.nlm.nih.gov/Omim), lists oodles of human traits (and disorders) caused by differences in certain genes.
I searched the database using the word “amylase”--and learned that there are many small variations, between people in the gene that makes the amylase enzyme. But I didn’t find any mention of saliva containing nary a dribble of the stuff. I may never know the answer to my mom’s saliva status. In any case, I soon moved on--lured hither and thither on the database by other fun and less-obvious-than-eye-color traits that run in families and appear to be controlled by genes.
Did you know that some people can’t smell freesias? Or that about 50% of us can’t smell a hormone called androstenone? (As for the rest, 15% of us find the smell OK or even nice, while 35% find it absolutely foul. More pleasantly, I read that when most folks eat an artichoke, and then drink water, the water tastes sweet. (I know it does for me.) And that the shape of one’s earlobes is a trait that runs in families. Some folks have nice, “free” earlobes that hang down while others have a so-called attached lobe.
My family, it appears, has an attached earlobe trait: Both myself and my younger brother, Ben, lack hanging-down lobes. Ben isn’t partial to his lobes. When his daughters were born, their ears were the first thing he checked (and he was delighted to see that he hadn’t passed on the trait).
Hairlines (straight or V-shaped), dimples (present or absent), hairy ears, the way one clasps one’s hands (left thumb on top or right thumb on top) dry or wet earwax--such traits are the fodder of introductory genetics classes and were at one time of keen interest to geneticists trying to figure out how traits were inherited in human beings.
(If you delve way back in the literature, you’ll find lots of research papers with titles like: “Further Observations on Ear Lobe Attachment” or “Preferences for Handedness, Arm Folding, and Hand Clasping in Families.”)
The scientists didn’t always get things right.
Take tongue-rolling, the ability to curl up the left and right edges of the tongue to make kind of a sausagey tube. It’s an archetypal genetics class example of a simply inherited, dominant genetic trait, one that was described way back in the 1940s.
But scientists now doubt that the trait is that simply controlled and think that learning, not just genes, may play a big part. Don’t hold your breath for a speedy resolution: Tongue-rolling, we’ll hazard, isn’t high on the nation’s research agenda.
Inspired by McKusick’s database and the knotty tongue-rolling issue, I decided to gather my own family history on tongue-rolling. I now have a newfound respect for the scientists who study inherited traits. “Can you roll your tongue?” I asked my father, mother and brothers (but not my sister, who doesn’t believe in computers or even, for that matter, having a phone that works).
I encountered confusion (“I am not sure what is involved,” replied my dad, the brilliant astrophysicist), vacillation (first my mom said she could--but then tried and failed) and amusing remarks (“Yes, I can roll my tongue, but not my Rs,” wrote brother Jon; “I sure can wag my tongue,” wrote Ben.)
That night, Ben, wife and two daughters had a tongue-rolling session over dinner and discovered that all of them except little Ruthie could roll their tongues on demand--but even Ruthie, when presented with a vegetarian sausage, said “Yuk!” and curled her tongue up at each edge.
I don’t know what to make of this family pattern--and, since I have not controlled for the awesome power of soy products, I must regrettably abandon the analysis
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If you have an idea for a Booster Shots topic, write or e-mail Rosie Mestel at the Los Angeles Times, 202 W. 1st. St., Los Angeles, CA 90012, rosie.mestel@latimes.com.
