Mutations: Genetic Variation Over Time
Summary / Students will investigate the differences that exist in the DNA sequence of the PTC taste receptor gene from humans and non human primates and determine whether the taster sequencechanged to the non-taster or vice versa. Students will understand that mutations allow genetic variations to develop over time and that a close genetic relationship exists between humans and non human primates.LS (9-11) 3-6; 6a / Background Information
Scientists can now compare the PTC receptor DNA sequence from humans to that of non-human primates and begin to determine if humans evolved the ability to taste bitter compounds or if we have evolved to be non-tasters
Materials / - computer
- projector
- worksheets and/or workstations
Engage / Ask the class: We have been examining PTC taste receptor DNA sequences from two different people. Is it possible to determine whether the taster sequence changed to the non-taster or vice versa? Can you propose a way to determine this? What species are most closely related to humans? What data would we need from non human primates to determine if some humans have evolved the ability to taste PTC or lost the ability to taste PTC?
Predict / What can DNA sequence comparisons tell us about our common ancestor?
Explore / Please compare PTC taste receptor DNA sequences of a human taster, a human non taster and non-human primates.
At each of the different locations in the gene, which human sequence matches the sequence of non-human primates? / Worksheet or computer workstations
if available.
Explain
/ Based on the sequence data, can you predict our “ancestral state” for the PTC taste receptor? Can you predict if the common ancestor of humans and non-human primates had the ability to taste the bitter compound PTC?Can you predict if humans have evolved the ability to taste bitter compounds or have evolved to be non-tasters?
How does DNA evidence support your interpretation?
Predict 2
/ From data presented on DNA sequence of the PTC taste receptor, is it possible to determine if bonobos, chimps and gorillas can taste PTC? Why or why not?What would scientists need to do to determine if non-human primates are tasters or non-tasters?
Taste tests using PTC in non human primates have been done. Since we cannot work with non-human primates in class, studies have shown that chimps also differ in their sensitivity to PTC.
Explore 2
/ How is it possible that chimps differ in their ability to taste PTC if the sequences examined all match that of human tasters?What data is missing? Do we have complete DNA sequences of the PTC taste receptor gene?
Study the sequence alignments comparing PTC DNA from human non-tasters, human tasters and chimps.
What differences do you observe? How many differences exist between humans (either taster or non-taster) and chimps?
Can you predict why some chimps do not taste PTC? How would DNA evidence support your prediction?
What experiment or study would you design to investigate your prediction? / Worksheets or workstations if available.
Wrapup