Embedded Files
Title: Supertasters - PTC Paper
Begin filling out the chart about yourself in the link below:
Principles Investigated & Topics: Genes, Traits, Heredity, Genotype & Phenotype, Recessive & Dominant Traits, Probability & Prediction, Chemical Defenses, Sensory Neurons, Genetic Diversity, Variation
CA Content Standards for Science: Biology
Genetics
3. a-c A multicellular organism develops from a single zygote, and its phenotype depends on its genotype, which is established at fertilization.
4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism.
Physiology
9.e Students know the roles of sensory neurons, interneurons, and motor neurons in sensation, thought, and response.
Materials: PTC Paper, Control Paper, Red Cups, Blue Cups, Handout and/or Google Doc, Powerpoint, Projector
Procedure:
1. Ask students to fill in information about themselves and make a prediction based on the information in the powerpoint and their own results as to whether they believe they are a supertaster, taster, or nontaster.
2. Pass out the blue cups with the control paper and ask each student to place one piece of paper on their tongue for a few moments and then remove the paper. Ask students to note the way the untreated paper tasted in preparation for the actual PTC paper.
3. Pass out the red cups with the PTC paper and ask each student to place one piece of paper on their tongue for a few moments and then remove the paper. Ask students to tell a partner how the paper tasted and return to their original hypothesis to determine whether they were accurate.
Student Prior Knowledge: Students should have a basic understanding of phenotype and how it depends on the genotype of the organism. They should know genes are found on the DNA located inside the nucleus of eukaryotes. Students should know a trait may have many different alleles and while some have true dominance others are more complicated. They should also know how to construct and interpret a Punnett square for genetic possibilities among the offspring. Students should know why approximately half of an individual's DNA sequence comes from each parent.
Explanation: In this demonstration the students will determine whether they possess the gene for tasting phenylthiocarbamide (PTC), a chemical adaptation found in plants to deter consumers. The trait for tasting PTC is dominant and allows organisms with the ability to taste the chemical to avoid plants which may be toxic. Many herbivores, in which plants are the primary source of food, have lost the ability to taste PTC. The information gathered from each student may be used to estimate their genotype and will not be entirely accurate.
PTC Paper:
Questions & Answers:
1. Why are supertasters less likely to smoke or drink alcohol?
Supertasters have a strong reaction to bitter tastes due to the ability to taste PTC and generally have more papillae on their tongues which contain the taste buds. The taste of cigarettes are bitter and would be extremely so for a supertaster as well as alcohol which may bother and burn the papillae.
2. Would a cow or a lion be more likely to be a supertaster? Explain.
The lion would be more likely to be a supertaster than the cow for a few reasons. The cow's primary source of food is grass and must be able to eat the plant without a significant negative reaction to the taste. The lion would have less tolerance for toxins in the plants and typically only consumes plants through the digestive system of its prey.
3. Why is the gene for tasting PTC a process of natural selection?
The more advantageous traits for an organism in a particular environment are passed on in a population to increase fitness and survival. The ability to taste PTC in humans demonstrates a process of natural selection because those individuals who could discern between bitter, toxic plants and nontoxic plants survived and reproduced. The trait for the ability to taste PTC is therefore dominant and the inability to taste recessive.
Applications to Everyday Life:
1. Persons who have the https://sites.google.com/site/sed525s12/spring-2012-demonstrations/demonstration-laura-millerability to taste PTC often dislike the taste of broccoli, cauliflower, spinach, and kale due to an overwhelming bitter taste (Negri, 2011).
2. Persons who have the ability to taste PTC is linked to increased emotional responses, either negative or positive, possibly due to their highly negative reaction to the taste of some foods (Macht, 2007).
3. Body Mass Index (BMI) is linked with the ability to taste PTC, possibly because persons choose less healthy food options and require more sodium in order to make foods taste better (Padiglia, 2010)
Videos:
http://www.khanacademy.org/science/biology/v/punnett-square-fun
http://www.khanacademy.org/science/biology/v/introduction-to-heredity
http://www.youtube.com/watch?feature=player_detailpage&v=2Fhc0t_QNhs
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