For a reason not yet clearly understood, some people can taste a certain bitter flavor while others cannot.
The cause has something to do with natural selection, the way that nature preserves particular traits, according to research by the University of Utah and the National Institutes of Health.
A compound called phenylthiocarbamide (PTC) embodies this flavor, described by those who can sense it as quite unpleasant. About three-quarters of all people can taste PTC while the rest can't.
"We really do find that some people can't taste it at all, and to others, it's intolerably bitter," said Stephen Wooding, a post-doctoral fellow at the Eccles Institute of Human Genetics in the U.'s School of Medicine.
The inability to taste substances like PTC may have a connection to smoking. An earlier study by the National Institute on Alcohol Abuse and Alcoholism found that the percent of smokers who couldn't taste PTC is considerably higher than that of the population as a whole.
The report by Wooding and colleagues, published in the American Journal of Human Genetics, examines the genes involved in the ability to taste PTC.
Oddly, in a taste test among Deseret Morning News reporters, a photographer and a reporter's wife, the normal ratio was reversed. When they placed on their tongues paper strips that had the PTC flavor, about three-quarters couldn't taste the substance.
Lois Collins, the only reporter to taste it among several tested, offered this description: "It's bitter. It's nasty bitter. It's el-sucko bitter."
That some people can taste PTC and others can't has been known since a geneticist named Arthur L. Fox announced the discovery in 1932. He was pouring a quantity of PTC, in the form of dust, into a bottle. Some of the dust blew around the lab, Fox reported in a paper.
Another occupant of the laboratory complained of the dust's bitter taste while Fox did not taste it. Further tests showed that most people could taste it but some could not.
Last year, a team at the U. led by Mark F. Leppert of the medical school and Dennis Drayna of the National Institutes of Health pinpointed the gene that accounts for the ability or inability to taste PTC.
The latest study is a follow-up to the genes' identification.
"We wanted to know about the evolution of this gene, so we sampled many people from around the world and looked at patterns of diversity in the gene," Wooding said.
There are two main types of this gene: the taster variant and the non-taster variant. Each person inherits two of the gene, which can be of either variant or both the same. By studying DNA, a researcher can tell which type or types the subject has.
The PTC gene is among approximately 24 involved in tasting bitter substances, according to the U.
The university maintains a library of DNA samples from people throughout the world. U. and NIH experts searched the genetic variations concerning PTC tasting, examining the area of DNA that was pinpointed by Leppert's group. They used samples from 165 people — 31 Africans, 69 Asians, 55 Europeans or Utahns of European descent and 10 American Indians.
"Among Europeans we find that 60 to 70 percent of people can taste it and from 30 to 40 percent cannot," Wooding said.
"There's not much geographical difference," he added. However, "there seems to be an unusually high number of Native Americans who are able to taste the substance."
The researchers think one variant of the gene is targeted toward detecting a particular bitter taste (including PTC). The second type is similar, but not identical, probably identifying different bitter compounds.
When people inherit one gene of each type they may have a better ability to taste a wide variety of bitter flavors. If they inherit two of the type most likely to detect PTC, they are able to taste it strongly. If they inherit two genes of the second type, they are unable to taste PTC.
The gene may not be as important as it once was in terms of warning that we should not snack on certain wild plants. However, it remains important from a medical standpoint.
According to Wooding, "It might predict things like your tendency to smoke and aspects of your diet."
E-mail: bau@desnews.com