To Taste, Or Not To Taste? 2010
Name: _____________________ Period: ____
Purpose/Objectives:
For this activity, you will determine your phenotype for a simple Mendelian trait: the
ability to taste the chemical PTC. You will also inventory the trait in your family members and
build a tasting phenotype pedigree. Once you have determined your phenotype, you will make
predictions about your genotype.
Background:
The gene that codes for the ability to taste a bitter chemical, phenylthiocarbamide (PTC)
has two alleles, a taster allele (T) and a non-taster allele (t). In mammals this is a diploid gene,
which means that every individual has two copies of this gene, or two alleles. A taster or nontaster phenotype is determined by the genotype. Each person’s genotype is determined by the
alleles they posses. A homozygous dominant genotype consists of two taster alleles and
results in a "strong-taster" phenotype. A heterozygous genotype consists of one taster allele
and one non-taster allele, causing a "weak-taster" phenotype. A "non-taster" phenotype only
results from a homozygous recessive genotype of two non-taster alleles.
Pre-Lab Questions:
1. How many possible phenotypes are there for the ability to taste and not taste PTC?
___________________________________________________________
2. How many possible genotypes are there for the PTC gene?
___________________________________________________________
3. Which alleles does a strong taster possess?
___________________________________________________________
4. Which alleles does a weak taster possess?
_____________________________________________________________
Methods/Procedure:
1. Obtain 1 piece of PTC test paper.
2. Place the paper on your tongue, do not chew or eat it.
3. If you cannot taste something bitter right away, wait one full minute.
4. Record your result (strong-taster, weak-taster, or non-taster) and discard the test paper.
5. Repeat steps 1-4 with members of your family.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
To Taste, Or Not To Taste? 2010
Name: _____________________ Period: ____
Results:
You
Parent
Parent
Sibling
Sibling
Grand- Grand- Grand- Grandparent parent parent parent
PTC
Phenotype
Post-Lab Questions:
1. Record your phenotype (strong, weak, or non-taster). ______________________________
2. Predict your tasting genotype (TT, Tt, tt). __________________________________________
3. What is an adaptation?
____________________________________________________________________________
____________________________________________________________________________
4. How might the ability to taste bitter chemicals be considered an adaptation?
____________________________________________________________________________
____________________________________________________________________________
5. In the space below, draw a pedigree of your family’s PTC tasting trait.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine