On Feb. 10, the Day of Learning in Community, Dr. Sara Tolsma will hold a session on genetic testing. Those who have chosen to participate in the testing will learn what their genotype and phenotype are at the PTC locus, as well as how the genes they carry affect whether or not they can taste phenylthiocarbamide, a harmless chemical.
“We all have a gene on both copies of our chromosome 7,” Tolsma said. She explained how we receive one chromosome 7 from our biological mother and one from our biological father, inheriting a copy of this gene from each parent.
“The gene comes in two forms, a ‘taster’ form and a ‘non-taster’ form,” Tolsma said. These forms are called alleles and the position on the chromosome is called a locus. Because we inherit two copies, our locus has two possible alleles. “If a person inherits two copies of the non-taster allele, they cannot taste the harmless chemical PTC,” Tolsma said. If they inherit one or two copies of the taster allele, they can.”
Students who have taken Dr. Tolsma’s BIO202 Genetics class will be familiar with the testing. Tolsma explained that they perform the testing to illustrate and practice several things, such as good pipetting skills, gel loading technique, polymerase chain reaction, and restriction enzyme cutting.
In the process, Dr. Tolsma and students isolate DNA from check cells and amplify part of the locus on chromosome 7 using a technique called polymerase chain reaction (PCR).
“We take the amplified DNA and cut with a restriction enzyme Hae III,” Tolsma said. “Hae III cuts DNA only if it ‘sees’ the sequence GGCC. Only the taster allele has GGCC in the amplified DNA.” In contrast, the nontaster allele has GGGC.
On Friday, Jan. 29, students interested in participating donated saliva samples. One such student was freshman Alli Derr, who explained that the process of donating was quite simple, taking around five minutes.
“First, we had to sign a waiver,” Derr said. “Then we created a four digit code so that we can see whether our test came out positive or negative for the locust during Dr. Tolsma’s presentation. Then we swished a salt mixture around in our mouth for a minute and then spit into a cup labeled with our number, and that’s it!”
Derr wanted to participate in the testing because she has always been fascinated with genetic testing and wanted to know how it works.
“As a participant, I was able to see how they collect samples and realize how far technology’s come so that we can now do genetic testing right here on our campus,” Derr said. “I also have never had part of my DNA tested, so it was a cool way to be introduced to the idea in a simple, and free, test.”