Bird Brains || Student Handout
Predicting Evolutionary Relationships
On the surface, mushrooms and monkeys don’t seem
to have much in common. But at the genetic level,
these two organisms aren’t so different after all.
Monkeys, mushrooms, and just about all other living
creatures have a gene that codes for a protein called
Cytochrome C, which plays a central role in releasing
energy from food. Genes and proteins that govern
such basic survival functions tend to be shared by
many organisms, making them an ideal tool for
scientists who want to learn more about relationships
among species. In this activity, you will use
Cytochrome C data to predict evolutionary
relationships between humans and six other species.
Procedure
1 Brainstorm some of the similarities and differences
between humans and each of the organisms
below. What are some of the criteria scientists
might use to determine how closely related,
in evolutionary time, two organisms are? Discuss
with a partner and share your ideas with the class.
Questions
Write your answers on a separate sheet of paper.
2 Predict how recently humans shared a common
ancestor with each organism listed below. Write
your predictions in a paragraph and explain your
reasoning, including the criteria you discussed in
Step 1 above. Consider features that humans share
with each organism, as well as ways in which
humans differ from each one.
3 Compare the Cytochrome C amino acid sequence
in humans to each of the organisms listed below.
You will find amino acid data on the Amino Acids
in the Protein Cytochrome C table on the next page.
For each organism, circle each amino acid that
differs from the human sequence.
Note: “*” indicates an amino acid that is missing
in some species. In places where one species has
“*” and the other has a letter, count that as a
difference.
4 Write down the number of differences between
a human and a:
tuna
gray whale
1 Based on the amino acid sequence data you
collected, which organism are humans most
closely related to? Which organisms are humans
most distantly related to? Explain your reasoning.
2 What additional data or information might help
you confirm the statement you made above?
3 Does your answer to Question 1 above match
the prediction you made in Step 2 of the
Procedure? Explain your answer.
4 Explain how amino acid sequence data can help
scientists infer patterns of evolutionary
relationships between species.
Who’ s my close s t rel ative?
According to evolutionary theory, species that
recently shared a common ancestor have more
similarities in their DNA than ones that last
shared a common ancestor long ago. By
comparing the order of amino acids that make
up the protein Cytochrome C and noting the
differences in the arrangement, scientists can
infer relationships among species. In general, the
more amino acids two species share, the more
closely related they are in evolutionary time.
snapping turtle
rhesus monkey
chicken/turkey
Neurospora (a type of bread mold)
© 2008 WGBH Educational Foundation.
Bird Brains || Student Handout
Amino Acids in the Protein Cytochrome C
Note: letters in boldface represent amino acids that are identical in all species. Asterisks represent positions that do not have an amino acid present,
so when comparing two species’ sequences, count as a difference any position in which one species has a letter and the other has an asterisk.
V
V
V
V
V
I
S
V
A
A
A
E
A
E
E
E
E
K
E
K
E
K
K
K
K
K
K
K
K
K
K
N
K
G
G
G
G
G
G
G
G
G
G
G
K
K
K
K
K
K
A
K
A
K
A
K
K
K
K
K
K
N
K
T
K
T
I
T
I
I
I
I
L
I
L
I
L
F
F
F
F
F
F
F
F
F
F
F
I
V
V
V
I
V
K
V
K
V
K
M
Q
Q
Q
M
Q
T
Q
T
Q
T
K
K
K
K
K
K
R
K
R
R
R
C
C
C
C
C
C
C
C
C
C
C
S
A
A
A
S
S
A
A
E
A
A
Q
Q
Q
Q
Q
Q
E
Q
L
Q
E
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
T
T
T
T
T
T
G
T
T
T
T
V
V
V
V
V
V
E
V
V
V
I
E
E
E
E
E
E
G
E
E
E
E
K
N
K
K
K
K
G
K
K
A
A
G
G
G
G
G
G
N
G
G
G
G
G
G
G
G
G
G
L
G
G
G
G
K
K
K
K
K
K
T
K
P
K
P
H
H
H
H
H
H
Q
H
H
H
H
K
K
K
K
K
K
K
K
K
K
K
T
V
T
T
T
T
I
T
V
V
V
G
G
G
G
G
G
G
G
G
G
G
P
P
P
P
P
P
P
P
P
P
P
N
N
N
N
N
N
A
N
N
N
N
L
L
L
L
L
L
L
L
L
L
L
H
W
H
N
H
H
H
H
H
H
H
G
G
G
G
G
G
G
G
G
G
G
L
L
L
L
L
L
L
L
I
F
I
F
F
F
I
F
F
F
F
F
Y
F
G
G
G
G
G
G
G
G
G
G
S
R
R
R
R
R
R
R
R
R
R
R
K
K
K
K
K
K
K
K
H
K
H
T
T
T
T
T
T
T
T
S
T
S
G
G
G
G
G
G
G
G
G
G
G
Q
Q
Q
Q
Q
Q
S
Q
Q
Q
Q
A
A
A
A
A
A
V
A
A
A
A
P
E
V
E
P
E
D
P
Q
P
Q
G
G
G
G
G
G
G
G
G
G
G
Y
Y
F
F
Y
F
Y
F
Y
F
Y
S
S
S
S
S
S
A
S
S
S
S
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
D
D
D
D
D
D
D
D
S
N
S
Amino Acid Position
* * * * * G
* * * * * G
* * * * * G
* * * * * G
* * * * * G
* * * * * G
* G F S A G
* * * * * G
T E F K A G
* G V P A G
P A P F E O G
* * G V P A GD V E K G K K I F V Q R C A Q CH T V E A G G K HK V G P N L HG L F G R K T G Q A A G F A Y
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
T
T
T
T
T
T
T
T
T
S
T
T
A
D
D
E
A
D
D
D
D
N
D
N
N
N
N
N
N
N
N
N
N
N
N
N
K
K
K
K
K
K
K
K
I
K
K
K
N
S
N
N
N
N
Q
N
K
A
R
A
K
K
K
K
K
K
K
K
K
K
A
K
G
G
G
G
G
G
G
G
N
G
G
G
S = Serine
C = Cysteine
H = Histidine
A
A
A
A
A
A
A
A
A
A
A
A
I
I
I
I
I
I
I
I
V
I
V
I
I
V
T
T
T
T
T
T
L
T
E
T
WG
WN
WG
WG
WG
WG
WD
WG
WD
WG
WA
WQ
D
D
E
E
D
D
N
E
N
D
P
D
T
T
T
T
T
T
T
T
N
T
T
T
L M
L M
L M
L M
L M
L M
L F
L M
M S
L F
M S
L F
E
E
E
E
E
E
E
E
E
E
D
E
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
N = Asparagine
T = Threonine
D = Aspartic Acid
E
N
E
E
E
E
E
E
E
D
E
D
L
L
L
L
L
L
L
L
L
L
L
L
E
E
E
E
E
E
E
E
T
E
E
E
N
N
N
N
N
N
N
N
N
N
N
N
P
P
P
P
P
P
P
P
P
P
P
P
K
K
K
K
K
K
K
K
K
K
K
K
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
I
I
I
I
I
I
I
I
I
I
I
I
P
P
P
P
P
P
P
P
P
P
P
P
I = Isoleucine
P = Proline
V = Valine
K
K
K
K
K
K
K
K
K
K
K
K
G
G
G
G
G
G
G
G
G
G
G
G
T
T
T
T
T
T
T
T
T
T
T
T
K
K
K
K
K
K
K
K
K
K
K
K
M
M
M
M
M
M
M
M
M
M
M
M
I
I
I
I
I
I
A
I
A
V
A
I
V
A
A
A
V
A
G
A
G
A
G
A
G
G
G
G
G
G
G
G
G
G
G
G
I
I
I
I
I
I
L
I
L
L
L
L
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
K
D
K
E
A
A
P
E = Glutamic Acid
K = Lysine
Q = Glutamine
F
F
F
F
F
F
F
F
F
F
F
F
E
G
G
A
E
S
K
G
K
N
K
N
E
E
E
E
E
E
D
E
D
E
D
E
R
R
R
R
R
R
R
R
R
R
R
R
D
D
D
D
D
D
D
D
D
D
D
D
L
L
L
L
L
L
I
L
L
L
L
L
I
V
I
I
I
I
I
I
I
I
V
I
A
A
A
A
A
A
T
A
T
A
T
A
Y
Y
Y
Y
Y
Y
F
Y
Y
Y
Y
Y
W = Tryptophan
F = Phenylalanine
L = Leucine
A
Q
A
A
A
V
N
E
N
A
N
G
L
L
L
L
L
L
M
L
L
L
M
L
K
K
K
K
K
K
K
K
K
K
L
K
K
S
K
D
K
D
E
K
K
E
E
S
T
T
T
T
T
T
T
T
C
T
S
T
N
S
N
S
N
S
A
N
E
K
K
K
E
*
E
K
E
K
E
*
*
*
*
*
R = Arginine
Y = Tyrosine
A
A
A
A
A
A
A
A
A
S
A
A
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112
*
*
*
*
*
*
*
*
*
*
*
*
Human
Tuna
Gray whale
Snapping turtle
Rhesus monkey
Chicken, Turkey
Neurospora
Pig, cow, sheep
Baker’s yeast
Silkworm moth
Candida
Screwworm fly
Human
Tuna
Gray whale
Snapping turtle
Rhesus monkey
Chicken, Turkey
Neurospora
Pig, cow, sheep
Baker’s yeast
Silkworm moth
Candida
Screwworm fly
Amino Acid Symbols
A= Alanine
G = Glycine
M = Methionine
© 2008 WGBH Educational Foundation.