Evolution: Possible Free-Response Questions
1. Genetic variation (the nonconstancy of species) is the raw material for evolution. Explain TWO cellular
and TWO molecular mechanisms that introduce variation into the gene pool of a population.
2. Describe the modem theory of biological evolution and discuss how it is supported by evidence from
each of the following areas:
(a) Fossil record
(b) Molecular biology
(c) Comparative anatomy
(d) Comparative embryology
(e) Bacterial resistance to antibiotics
3. On the archipelago of the Galapagos Islands, which most geologists believe to be of volcanic origin
without ever having had any land connection with the west coast of South America, Darwin discovered a
group of small finches. These birds have since been classified into more than a dozen species. These birds
have differences, particularly in their adaptations for food-getting. It is believed that all these species are
descendants of a single species which migrated from the mainland. On the mainland there has never been
more than a single species even though the rate of mutations is thought to be the same in both locations.
(a) Explain how each of the following could have played a role in the development of the many
species of Galapagos finches:
- the bottleneck effect
- genetic drift
- geographic isolation
- unoccupied ecologic niches
(b) Explain why the mainland species has not differentiated into more than one species
OR
why has speciation not occurred at the same rate on the mainland as it has on the islands?
4. Darwin is considered the “father of evolutionary biology.” Four of his contributions to the field of
evolutionary biology are listed below.
- the nonconstancy of species
- branching evolution, which implies the common descent of all species
- occurrence of gradual changes in species
- natural selection as the mechanism for evolution
(a) For each of the four contributions listed above, discuss one example of supporting evidence
and give an explanation of each phrase.
(b) Darwin’s ideas have been enhanced and modified as new knowledge and technologies have
become available. Discuss how TWO of the following have modified biologists’ interpretations
of Darwin’s original contribution.
- Hardy-Weinberg equilibrium
- Punctuated equilibrium
- Genetic engineering
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5. Do the following with reference to the Hardy-Weinberg model.
(a) Indicate the conditions under which allele frequencies (p and q) remain constant from one
generation to the next.
(b) Calculate the frequencies of the alleles and frequencies of the genotypes in a population of
100,000 rabbits of which 25,000 are white and 75,000 are agouti (show all work).
(In rabbits the white color is due to a recessive allele, w, and agouti is due to a dominant allele, w +.)
(c) If the homozygous dominant condition were to become lethal, what would happen to the allelic,
genotypic and phenotypic frequencies in the rabbit population after two generations?
6. The human genetic condition sickle cell anemia results from a single base-pair mutations in DNA.
(a) Explain how a single base-pair mutant in DNA can alter the structure and function of a protein.
(b) Explain the potential consequences of the production of a mutant protein to the structure and
function of the red blood cells in a person with sickle cell anemia.
(c) Describe how the frequency of an allele coding for a mutant protein may increase in a
population over time and explain why the sickle cell allele is selected for in certain areas of the
world.
7. Phylogeny is the evolutionary history of a species.
(a) The evolution of a species is dependent on changes in the genome of the species.
Identify TWO mechanisms of genetic change, and explain how each affects genetic variation.
(b) Based on the data in the table below, draw a phylogenic tree that reflects the evolutionary
relationships of the organisms based on the differences in their cytochrome-c amino acid
sequences and explain the relationships of the organisms.
(c) Based on the data, identify which organism is most closely related to the chicken and explain
your choice.
(d) Describe TWO types of evidence (other than the comparison of proteins = comparative
biochemistry) that can be used to determine the phylogeny of organisms. Discuss one strength of
each type of evidence you described.
THE NUMBER OF AMINO ACID DIFFERENCES IN CYTOCHROME-c AMOUNG VARIOUS ORGANISMS
Horse
Donkey
Horse
Donkey
Chicken
Penguin
Snake
0
1
11
13
21
0
10
12
20
0
3
18
0
17
Chicken
Penguin
0
Snake
2
8. Phylogeny reflects the evolutionary history of organisms.
(a) Discuss TWO mechanisms of speciation that lead to the development of separate species from a
common ancestor.
(b) Explain THREE methods that have been used to investigate the phylogeny of organisms.
Describe a strength or weakness of each method.
(c) The two phylogenetic trees represent the relationship of whales to six other mammals. All of the
organisms shown have a pulley-shaped astragalus bone in the ankle except for the whale.
• For each tree, describe a monophyletic group, the closest relative to the whale, and the point
at which the pulley astragalus was lost or gained.
• Based on the principle of parsimony (the simplest explanation is the best) and the genomic
information in the Tables 1 and 2, identify which tree is the best representation of the
evolutionary relationship of these animals, and justify your answer.
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Table 1. - Data on Presence of Specific DNA Sequences
+ sequence present
- sequence absent
? undetermined
Locus
Cow
Deer
Whale
Hippo
Pig
Peccary
Camel
1
+
?
?
-
2
+
?
-
3
+
+
?
?
-
4
+
+
?
-
5
+
+
?
-
6
+
?
-
7
+
+
?
+
?
?
-
8
+
?
+
+
?
-
9
+
+
+
+
?
?
-
10
+
+
?
-
11
+
+
?
?
?
-
12
+
+
+
+
+
?
-
13
+
+
-
Table 2. - DNA Fingerprint
Locus
Cow
Deer
Whale
Hippo
1
2
3
4
5
6
7
8
9
10
11
12
13
9. Discuss three things Charles Darwin never knew.
4
Pig
Peccary
Camel