Mutations: Genetic Variation Over Time
Worksheet
Scientists can now compare 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 nontasters.
Below are DNA nucleotide sequences at three different positions within the PTC taste receptor gene. Compare
the sequences of humans to those of three of our closest relatives among the primates.
Nucleotide
Position
Human
Taster
Human
Non-taster
Bonobo
Chimp
Gorilla
145
CCA
GCA
CCA
CCA
CCA
785
GCT
GTT
GCT
GCT
GCT
886
GTC
ATC
GTC
GTC
GTC
At position 145, which human sequence matches the sequence of non-human primates? Taster or non-taster?
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At position 785, which human sequence matches the sequence of non-human primates? Taster or non-taster?
________________________________________________________________________________________
At position 886, which human sequence matches the sequence of non-human primates? Taster or non-taster?
________________________________________________________________________________________
Based on the sequence data, can you predict our “ancestral state” for this receptor? In other words, can you
predict if the common ancestor of humans and non-human primates could taste the bitter compound PTC?
Have modern humans evolved the ability to taste bitter compounds or have we evolved to be non-tasters. Use
DNA evidence to support your prediction.
_______________________________________________________________________________________
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From the data presented on DNA sequence, is it possible to determine whether 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 test studies have shown that just like humans, chimps differ in their sensitivity to PTC.
How is it possible that chimps differ in their ability to taste PTC if the sequences examined (above) all match
that of human tasters?____________________________________________________________________
What data is missing? Have you examined the complete sequences of the PTC taste receptor gene? _________
On the following pages is a DNA sequence alignment comparing PTC DNA sequence from human non-tasters,
human tasters and chimps.
Study the sequences, 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?
___________________________________________________________________________________
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Chimp PTC
Human Non-Taster PTC
Human Taster PTC
ATGTTGACTCTAACTCGCATCCACA
ATGTTGACTCTAACTCGCATCCGCA
ATGTTGACTCTAACTCGCATCCGCA
25
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CTGTGTCCTATGAAGTCAGGAGTAC
CTGTGTCCTATGAAGTCAGGAGTAC
CTGTGTCCTATGAAGTCAGGAGTAC
50
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
ATTTCTGTTCATTTCAGTCCTGGAG
ATTTCTGTTCATTTCAGTCCTGGAG
ATTTCTGTTCATTTCAGTCCTGGAG
75
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TTTGCAGTGGGGTTTCTGACCAATG
TTTGCAGTGGGGTTTCTGACCAATG
TTTGCAGTGGGGTTTCTGACCAATG
100
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CCTTCGTTTTCTTGGTGAATTTTTG
CCTTCGTTTTCTTGGTGAATTTTTG
CCTTCGTTTTCTTGGTGAATTTTTG
125
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GGATGTAGTGAAGAGGCAGCCACTG
GGATGTAGTGAAGAGGCAGGCACTG
GGATGTAGTGAAGAGGCAGCCACTG
150
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
AGCAACAGTGATTGTGTGCTGCTGT
AGCAACAGTGATTGTGTGCTGCTGT
AGCAACAGTGATTGTGTGCTGCTGT
175
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GTCTCAGCATCAGCCGGCTTTTCCT
GTCTCAGCATCAGCCGGCTTTTCCT
GTCTCAGCATCAGCCGGCTTTTCCT
200
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GCATGGACTGCTGTTCCTGAGTGCT
GCATGGACTGCTGTTCCTGAGTGCT
GCATGGACTGCTGTTCCTGAGTGCT
225
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
ATCCAGCTTACCCACTTCCAGAAGT
_ATCCAGCTTACCCACTTCCAGAAGT
ATCCAGCTTACCCACTTCCAGAAGT
250
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TGAGTGAACCACTGAACCACAGCTA
TGAGTGAACCACTGAACCACAGCTA
TGAGTGAACCACTGAACCACAGCTA
275
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CCAAGCCATCATCATGCTATGGATG
CCAAGCCATCATCATGCTATGGATG
CCAAGCCATCATCATGCTATGGATG
300
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
ATTGCAAACCAAGCCAACCTCTGGC
ATTGCAAACCAAGCCAACCTCTGGC
ATTGCAAACCAAGCCAACCTCTGGC
325
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TTGCTGCCTGCCTCAGCCTGCTTTA
TTGCTGCCTGCCTCAGCCTGCTTTA
TTGCTGCCTGCCTCAGCCTGCTTTA
350
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CTGCTCCAAGCTCATCCGTTTCTCT
CTGCTCCAAGCTCATCCGTTTCTCT
CTGCTCCAAGCTCATCCGTTTCTCT
375
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CACACCTTCCTGATCTGCTTGGCAA
CACACCTTCCTGATCTGCTTGGCAA
CACACCTTCCTGATCTGCTTGGCAA
400
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GCTGGGTCTCCAGGAAGATCTCCCA
GCTGGGTCTCCAGGAAGATCTCCCA
GCTGGGTCTCCAGGAAGATCTCCCA
425
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GATGCTCCTGGGTATTATTCTTTGC
GATGCTCCTGGGTATTATTCTTTGC
GATGCTCCTGGGTATTATTCTTTGC
450
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TCCTGCATCTGCACTGTCCTCTGTG
TCCTGCATCTGCACTGTCCTCTGTG
TCCTGCATCTGCACTGTCCTCTGTG
475
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TTTGGTGCTTTTTTAGCAGACCTCA
TTTGGTGCTTTTTTAGCAGACCTCA
TTTGGTGCTTTTTTAGCAGACCTCA
500
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CTTCACAGTCACAACTGTGCTATTC
CTTCACAGTCACAACTGTGCTATTC
CTTCACAGTCACAACTGTGCTATTC
525
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
ATGAATAACAATACAAGGCTCAACT
ATGAATAACAATACAAGGCTCAACT
ATGAATAACAATACAAGGCTCAACT
550
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GGCAGATTAAAGATCTCAACTTATT
GGCAGATTAAAGATCTCAATTTATT
GGCAGATTAAAGATCTCAATTTATT
575
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TTATTCCTTTCTCTTCTGCTATCTG
TTATTCCTTTCTCTTCTGCTATCTG
TTATTCCTTTCTCTTCTGCTATCTG
600
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TGGTCTGTGCCTCCTTTCCTATTGT
TGGTCTGTGCCTCCTTTCCTATTGT
TGGTCTGTGCCTCCTTTCCTATTGT
625
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TTCTGGTTTCTTCTGGGATGCTGAC
TTCTGGTTTCTTCTGGGATGCTGAC
TTCTGGTTTCTTCTGGGATGCTGAC
650
Chimp PTC
TGTCTCCCTGGGAAGGCACATGAGG
675
Human Non-Taster PTC
Human Taster PTC
TGTCTCCCTGGGAAGGCACATGAGG
TGTCTCCCTGGGAAGGCACATGAGG
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
ACAATGAAGGTCTATACCAGAGACT
ACAATGAAGGTCTATACCAGAAACT
ACAATGAAGGTCTATACCAGAAACT
700
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CTCGTGACCCCAGCCTGGAGGCCCA
CTCGTGACCCCAGCCTGGAGGCCCA
CTCGTGACCCCAGCCTGGAGGCCCA
725
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CATTAAGGCCCTCAAGTCTCTTGTC
CATTAAAGCCCTCAAGTCTCTTGTC
CATTAAAGCCCTCAAGTCTCTTGTC
750
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
TCCTTTTTCTGCTTCTTTGTGATAT
TCCTTTTTCTGCTTCTTTGTGATAT
TCCTTTTTCTGCTTCTTTGTGATAT
775
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CATCCTGTGCTGCCTTCATCTCTGT
CATCCTGTGTTGCCTTCATCTCTGT
CATCCTGTGCTGCCTTCATCTCTGT
800
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GCCCCTACTGATTCTGTGGCGTGAC
GCCCCTACTGATTCTGTGGCGCGAC
GCCCCTACTGATTCTGTGGCGCGAC
825
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
AAAATAGGGGTGATGGTTTGTGTTG
AAAATAGGGGTGATGGTTTGTGTTG
AAAATAGGGGTGATGGTTTGTGTTG
850
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GGATAATGGCAGCTTGTCCCTCTGG
GGATAATGGCAGCTTGTCCCTCTGG
GGATAATGGCAGCTTGTCCCTCTGG
875
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GCATGCAGCCGTCCTGATCTCAGGC
GCATGCAGCCATCCTGATCTCAGGC
GCATGCAGCCGTCCTGATCTCAGGC
900
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
AATGCCAAGTTGAGGAGAGCTGTGA
AATGCCAAGTTGAGGAGAGCTGTGA
AATGCCAAGTTGAGGAGAGCTGTGA
925
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CGACCATTCTGCTCTGGGCTCAGAG
TGACCATTCTGCTCTGGGCTCAGAG
TGACCATTCTGCTCTGGGCTCAGAG
950
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
CAGCCTGAAGGTAAGAGCCGACCAC
CAGCCTGAAGGTAAGAGCCGACCAC
CAGCCTGAAGGTAAGAGCCGACCAC
975
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
AAGGCAGATTCCCGGACACTGTGCT
A A G G C A G A T T C C C G G A C A C T G T G C T 1000
AAGGCAGATTCCCGGACACTGTGCT
Chimp PTC
Human Non-Taster PTC
Human Taster PTC
GA
GA
GA
1025