Download Formal Outline Introduction The Founding of PTC When Who How

Formal Outline
I.
Introduction
II.
The Founding of PTC
a. When
b. Who
c. How
III.
Significant PTC Testings
a. Ford, Fisher, Huxley
IV.
TAS2R38
V.
Conclusion
Background Research
Phenylthiocarbamide, also known as phenylthiourea, and more commonly PTC, is an
organic compound that allows the holder of a specific gene to taste the compound as bitter,
slightly bitter, or completely tasteless. Respectively, these people are known as “tasters” and
“nontasters.” Approximately 75% of Earth’s population can taste PTC, whereas 25% cannot.
PTC was first discovered in 1931 when chemist Arthur L. Fox accidentally released a
cloud of finely-powdered PTC into the air. A near-by colleague, whose exact identification is not
known but is suggested to be C.R. Noller (A 75 Year Adventure, 1), complained of a great bitter
taste in the air. Fox immediately became confused. Because Fox was closer to where the accident
occurred, he himself should have tasted a more intense taste of the compound, yet he repeatedly
insisted on tasting nothing. Motivated by this reason, Fox continuously conducted experiments
on himself, his near-by colleague, family members, friends, and co-workers. After several tests,
Fox came to the conclusion that the ability to taste PTC disregarded age, sex, and many other
factors. After this occurrence, Fox documented and published his discoveries. Fox’s work
became famous almost immediately, causing him to receive world-wide attention.
Without realizing it, Fox had set the basis for future genetic studies. Many more scientists
after him became curious of the new development in science called genetics, including R.A.
Fisher, E.B. Ford, and Julian Huxley. All three scientists were delegates to the Seventh
International Congress of Genetics that was assembled in Edinburgh, Scotland during August of
1939. Although the meeting was deemed “of no great significance” (A 75-Year Adventure, 3) for
numerous reasons, Fisher, Ford, and Huxley were able to obtain data that produced even greater
interest in PTC sensitivity.
Because Europe was on the brink of war, non-Scottish delegates, especially Dutch and
German, were forced to leave the convention beforehand. R.A. Fisher, hailing from England,
was forced to leave Edinburgh, but not before testing PTC solutions on eight chimpanzees and to
one orangutan “in the form of a drink” (A 75-Year Adventure, 4) at the Edinburgh Zoo.
Furthermore, more chimpanzees were tested on September 25 and October 1 at the London and
Whipsnade Zoo.
In total, 27 chimpanzees were tested during Fisher, Ford, and Huxley’s experiments. “Of
the 27 chimpanzees tested, 20 were tasters and 7 were nontasters, implying allele frequencies of
49 and 51% for the taster and nontaster alleles, respectively – frequencies nearly identical to
several studies in humans.” (A 75-Year Adventure, 4)
Because of the data acquired by Fox and Fisher, Ford, and Huxley, geneticists today have
been able to determine that “there is an inherited component that influences how humans taste
PTC.” (Genes and Bitter Taste, 1) Geneticists discovered the gene that allows a person to be
PTC-sensitive or not, TAS2R28, in 2003, and although PTC is considered as a “dominant
genetic trait” (PTC Testing, 1), it is the gene TAS2R38, which is located on chromosome 7, that
grants a being ability to taste PTC or not. “There are two common allele forms of the PTC gene:
one of them is a tasting allele, and the other is a non-tasting allele. Each allele codes for a bitter
taste receptor protein with a slightly different shape. The shape of the receptor protein
determines how strongly it can bind to PTC. Since all people have two copies of every gene,
combinations of the bitter taste gene variants determines whether someone finds PTC intensely
bitter, somewhat, or without taste at all.” (Genes and Bitter Taste, 1) Knowing this, geneticists
usually pay strong attention to taste intensity when testing humans on their PTC sensitivity: if a
being says the taste is strong, he or she has both tasting alleles; if the tasters says it is some-what
mild, he or she has one tasting allele and one non-tasting allele; and if the taster does not taste
anything, he or she has two non-tasting alleles, deeming him or her a nontaster.
As is obvious, the topic of PTC is one of great complexity. Geneticists today are still
trying to research PTC related complications such as how one actually acquires the gene
TAS2R38, and with new genetic discoveries being made every day, that research is near
impossible to do. When Arthur L. Fox released that cloud of finely-powdered PTC into the air at
his DuPont laboratory, all he thought of the incident was an accident, a mistaken even. Now,
almost 75 years later, what was then considered a mistake has been transformed into a gateway
into a branch of biology that is now known as genetics.
Bibliography and Works Cites
Anonymous. (n.d.) Phenylthiocarbamide. Retrieved
http://en.wikipedia.org/wiki/Phenylthiocarbamide
November,
23,
2011
from
Genetic Science Learning Center. (2011, January 24) PTC: Genetics and Bitter Taste. Retrieved
November 25, 2011 from http://learn.genetics.utah.edu/content/begin/traits/ptc/
Jenkins, M. (1998). Teach Yourself: Genetics. London, England: Hodder Headline Plc.
Mortens, E. (n.d.) Phenylthiocarbamide (PTC) Testing. Retreived November, 23, 2011 from
https://sites.google.com/a/luther.edu/genetics/students/erikmortens/phenylthiocarbamide-ptc-testing
Wooding, S. (2006, April) Phenylthiocarbamide: 75-Year Adventure in Genetics and Natural
Selection.
Retrieved
November
http://www.genetics.org/content/172/4/2015.full
27,
2011
from
PTC
Tracy Glova
Grade 8
Saint William School