Biology 112 – First Hour Exam                         Name_______________________

 

READ THESE INSTRUCTIONS: The test has three sections. You will answer all of the multiple choice and short answer questions from Sections I and II. You will answer one essay from Section III. Budget your time.

 

Section I (17 points) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

 

1. (1 Point) Researchers have found fossils of Eocene horse species in Colorado. Deeper deposits contain smaller species, and more recent deposits contain larger species. How does this observation support the theory of evolution?

A) It provides evidence that species change over time.

B) It shows that all species are related to each other.

C) It proves that environments have changed over time.

D) It suggests that species are unchanging and of recent origin.

E) It does not support the theory of evolution.

 

2. (1 Point) Which of the following is the best modern definition of evolution?

A) inheritance of acquired characters

B) descent without modification

C) change in allele frequencies in a population over time

D) survival of the fittest

 

3. (2 Points) A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies; but after several years, the farmer sees more and more pigweed, no matter how often he applies triazine. Which of these actions is most likely to solve the farmer's problem?

A) Trying a different herbicide

B) Increasing the amount of triazine he puts on his fields

C) Buying triazine from a different company

D) Adding triazine more often to his fields

 

4. (1 Point) On the tree of life, the branch leading to animals is closer to fungi than it is to the branch leading to land plants. Which of the following statements is correct?

A) Animals and land plants are more closely related to each other than either is to fungi.

B) Animals and plants do not have a common ancestor.

C) Fungi and animals do not have a common ancestor.

D) Animals and fungi are more closely related to each other than animals are to land plants.

 

5. (2 Points) An earthquake decimates a ground-squirrel population. The surviving population happens to have broader stripes on average than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?

A) Directional selection

B) Gene flow

C) Disruptive selection

D) A founder event

E) A genetic bottleneck

 

6. (2 Points) Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg model?

A) f(A1)  = 0.9600, f(A2)  = 0.0400

B) f(A1)  = 0.9800, f(A2)  = 0.0200

C) f(A1)  = 0.9700, f(A2)  = 0.0300

D) f(A1)  = 0.9997, f(A2)  = 0.0003

E) f(A1)  = 0.9604, f(A2) = 0.0392

     

 

 

7. (1 Point) Many crustaceans (e.g., lobsters, shrimp, and crayfish) use their tails to swim, but crabs have reduced tails that curl under their shells and are not used in swimming. This is an example of _________.

A) an extinction.

B) a vestigial trait.

C) artificial selection.

D) natural selection.

E) the law of succession.

 

8. (1 Point) Which of the following organisms would be most likely to fossilize?

A)  A common squirrel

B)  A common worm

C)  A rare squirrel

D)  A rare worm

 

9. (1 Point) Which of the following likely has the most Hox genes?

A) Slugs     B) Jellyfish        C) Bees            D) Dolphins

 

 

Figure 27.8 from your text

           

10. (2 Points) The graphs on the right show percentage of change in three different molecular sequences plotted against time. Which of these molecular sequences would make a good candidate for a molecular clock? 

 

A) Graph A, because the curve levels off over time

B) Graph B, because DNA is more important to organisms and therefore will give a more accurate picture of divergence

C) Graph C, because the change in sequence is the most rapid

D) Graph A or C, because changes in amino acid sequence are more likely to be neutral than changes in DNA

E) Graph B or C, because they are straight lines

 

 

 

 

 

 

 

 

11. (1 Point) Which of the following has the highest Darwinian fitness?

A) A scientist who devotes herself to science and wins the Nobel Prize

B) A woman who home schools her two children

C) A sperm donor who anonymously fathers 52 children

D) A personal trainer who works out at the gym every day

 

12.  (1 Point) Which of the following could be a vicariance event for species in that habitat?

A) The level of water in a lake recedes, creating two lakes where there used to be one.

B) Some insects get blown in a storm to a new mountain range, where they lay eggs.

C) All of the above could be vicariance events for species in that habitat.

13. (1 Point) Applying the principle of parsimony to the trait "ability to fly," which of the two phylogenetic trees above is better?

A) Tree 1                                                                                       B) Tree 2

 

Section II (68 Points). Short Answer. Answer all questions in this section.  You can be brief as long as you answer the question completely.

 

14. (5 Points) What are the necessary conditions for natural selection to occur within a population?

 

 

1.    Variation in a trait in the population

2.    The trait is heritable, at least to some extent

3.    Differential Reproductive success based on that trait

 

 

15. (4 Points) Martin Wikelski and L. Michael Romero (Body size, performance and fitness in Gal‡pagos marine iguanas, Integrative and Comparative Biology 43 [2003]:376-86) measured the snout-to-vent (anus) length of Gal‡pagos marine iguanas and observed the percent survival of different-sized animals. Figure 25.2 shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different size classes for males (solid) and females (dotted).

           

Which kind of selection is at work here? What effect does this kind of selection have on variation?

 

Stabilizing selection. Stabilizing selection tends to reduce variation in the population since variation away from the mean value is selected against.

 

 

 

16. (5 Points) Explain how the concepts of phenotype and genotype relate to natural selection.

 

The phenotype (all observable physical traits of an individual) is the physical expression of the genotype (genetic makeup of an individual). In terms of natural selection:

  1. Variation in genotype, along with environmental variation, produces variation in the phenotype.
  2. Heritability is a result of the genotype.
  3. Differential Reproductive success is a function of how the phenotype interacts with its environment.

 

 

 

 

 

 

 

 

 

17. (5 Points) Which force of evolution has the most influence on speciation and why?

 

Gene flow. Speciation is mainly the result of reproductive isolation. When there is no gene flow between populations (reproductive isolation), then the forces of mutation, drift, and selection can act independently on the separate, isolated populations. This causes each to have its own evolutionary trajectory.

 

 

18. (2 points) Cystic fibrosis is a genetic disorder in homozygous recessives (ff) that typically causes death in the early 30s. Over time, how do you expect the f allele frequency to change?

 

It will decrease, assuming that the disorder leads to reduced reproductive success.

 

 

 

19. (5 Points) Explain the statement ÒMutation proposes and selection disposesÓ.

 

Mutation is the source of all variation. It is the only source of new alleles. It is a random event. It can produce advantageous, neutral, and disadvantageous changes. In essence, it provides options. Natural selection is not random. It is a filtering process that eliminates disadvantageous changes in genes from the gene pool (and increases the frequency of advantageous geneotypes).

 

 

 

20. (4 Points) What are analagous traits and why are they considered evidence for evolution by natural selection? 

 

Analagous traits are similar traits shared by two species, but no ancestral form was present in a common ancestor. Analagous traits demonstrated that similar selective pressures produce similar morphologies. This is known as convergent evolution.

 

NOTE: it is wrong to say ÒAnalagous traits are similar traits in species without a common ancestorÓ. All species have a common ancestor. The difference here is whether or not the trait in question was present in a common ancestor.

 

 

 

21. (3 Points)  You sequence the genes that code for an important glycolytic enzyme in a moth, a mushroom, a worm, and an alga and find a high degree of sequence similarity among these distantly related species. How is this similar to the fact that he same basic internal organs (kidneys, stomach, heart, lungs) are found in frogs, birds, snakes. and rodents?

 

These are both examples of homologous traits. The first example is a genetic homology. The second demonstrates structural homologies.

 

 

 

 

22. (4 Points) For each of the following mechanisms of evolution, tell me whether that mechanism increases or decreases variation in a population:

 

a.    gene flow - INCREASE

 

b.    mutation - INCREASE

 

c.     genetic drift - DECREASE

 

d.    natural selection - DECREASE

 

 

 

23. (4 Points) Is sexual selection different from natural selection? Why or why not?

 

Sexual selection is selection on traits that increase success in competing for mating opportunities (i.e., mates). Sexual selection is a special case of natural selection, in that sexual selection arises when there is variation in that trait, the trait is heritable, and the trait bestows differential reproductive success. Although, traits arise through sexual selection that may be detrimental to survival, they endow the possessor with an advantage in gaining reproductive success – i.e., differential reproductive success based on that trait.

 

 

 

 

24. (3 Points) In 1986 a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in the surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. What would you expect to be the effect on variation in traits in the wild populations in the area?

 

The increased radiation may cause increased frequency of mutation. Therefore, you would expect increased variation in traits.

 

 

 

 

 

25. (4 Points) Why is allopatric speciation the most common process by which species arise?

 

In allopatric speciation, populations are separated by geographical barriers and reproductive isolation is easy to maintain due to the physical separation of the populations. The geographic barriers prevent gene flow and the forces of evolution act independently on each population, leading to speciation

 

 

 

 

 

26. (3 Points) What kinds of data would be useful in creating a phylogenetic tree of a related group of organisms? 

 

At least 2 of these dealing with the shared characteristics (homologies, etc.):

Morphological data from fossil species

Morphological data from living species 

Behavioral data from living species 

Genetic sequences from living species 

 

 

27. (5 Points) Variation in a trait can be partitioned into two categories. What are they and which of them is most important to the process of natural selection?

 

Total Variation = Environmental Variation + Genetic Variation. Genetic variation is most important because for natural selection to occur on a trait, the variation in a trait must be heritable (and produce differential reproductive success). If you said heritable and non-heritable, you received credit. If you had another, reasonable answer, you also received partial credit.

 

28. (6 Points) After the drought of 1977 on Daphne Major in the Galapagos, medium ground finches with large, deep beaks survived better than those with smaller beaks did because they could more easily crack and eat the tough Tribulus cistoides fruits. Tell me how you would expect bill depth to change over time if (A) drought conditions continue through many years and (B) a tourist company set up a series of permanent, reliable feeding stations with a variety of bird seeds (different types and sizes), so that tourists can get a better look at the finches.

 

A)   if drought conditions persist, the selective pressure for large, deep beak would increase. Thus, directional selection would occur resulting in an increase in mean bill size in the population over time.

B)   Increasing the variety of seed sizes and types would eliminate the selective advantage of large, deep beaks. Essentially, if there are seeds for all size beaks, all would survive equally well. Mean beak size would decrease from the post-drought size.

 

 

29. (4 Points) Which of the following isolating mechanisms are prezygotic and which are postzygotic? (Circle either PRE or POST) MAKE UP NEW ONES

 

A. Land iguana eggs can't be fertilized by marine iguana sperm.          

PRE                POST

 

B. Mules-horse-donkey hybrids-are sterile.                                                

PRE                POST

 

C. Female butterflies lay their eggs on vegetation. Males wait on the vegetation to fertilize In a meadow, one butterfly species lays its eggs on grasses and another butterfly species lays its eggs on pines.

PRE                POST

 

D. Three populations of crickets look very similar, but the males have courtship songs that sound different.

PRE                POST

 

SECTION III (15  points) Essay – answer ONE of the questions below. Your choice. Write your answers on the blank page attached.

 

30. Describe two ways that data from molecular biology have contributed to our understanding of evolutionary relationships among species.  Include one example of a relationship revealed by molecular data that comparisons of morphological phenotypes could not have given us.

 

Main Points:

1.   You could describe any of many molecular techniques, such as DNA sequencing, that let us see genetic relationships that we could not see before. Ideally, when you mention these, you would explain the concept of how they work (i.e., the similarity in base-pair sequences is an indication of how closely related two species might  be).

2.   You could describe a number of new ways in which such techniques have let us see these relationships – i.e., molecular clocks, evidence for gene-swapping (lateral gene transfer), the use of ssuRNA, or evidence for the Endosymbiotic Theory

3.   For part B., the most obvious answer is our understanding of the relationship between Archaea, Bacteria, and Eukaryotes and how that is different from the old 5-Kingdom model. Other appropriate answers, worked, too.

 

 

31. Use the example of herbicides to explain and illustrate DarwinÕs Theory of Evolution by Natural Selection.

 

Main points:

1.  Necessary conditions: variation in traits, heritability of traits, and differential reproductive success based on those traits.

2.  Should result in a change in gene frequency in a population over time.

3.  Illustrate with:

a.  Natural variation in resistance to herbicide. Farmers spray herbicide. Kill those unable to tolerate the herbicide.

b.  The resistance is heritable. If this resistance is due to a heritable trait, then the variation in resistance is passed on to offspring (heritability).

c.Only the resistant variant is able to reproduce (differential reproductive success due to differential survival). Thus, only genes for resistance are passed to the next generation.

d.  Proportion of genes in the population that are resistant to the herbicide changes over time from low percentage of the population to high proportion. Herbicides become less and less useful due to directional selection for herbicide resistance.

 

 

32. The Hardy-Weinberg equation is p2, + 2pq + q2 = 1. What are p and q? What are p2, 2pq, and q2? Why would an evolutionary biologist want to calculate these values? What conditions must be fulfilled for the Hardy-Weinberg Rule to apply?  For each of these, explain what evolutionary mechanisms can violate it.

 

Main Points:

1.    P and q are allele frequencies in a 1-locus, 2 allele system, thus p=q =1.

2.    p2, 2pq, and q2 are all possible genotype frequencies.

3.    An evolutionary biologist would calculate these values to test for the effect of evolution on a population. This is because Hardy-Weinberg serves as a null model – it lets us predict gene frequencies in a population in the absence of evolution. The predicted frequencies should not change over time (generations).

4.    It assumes the following about a population: no mutation, no migration, no genetic drift, no selection, random mating.

5.    Can be violated when:

a.    Small population size, since genetic drift is a function of chance alone. Thus, a very large population would be necessary for a situation where the H-W rule might apply. Populations that undergo a bottleneck or the founder effect would be small and, thus, violate the rule.

b.    Mutations are a random byproduct of gene duplication and thus are almost impossible to keep out of a population.

c.     There can be no migration between populations (gene flow).

d.    Sexual selection is one way to violate the assumption of random mating.

e.     No selection means that every organism has an equal probability for survival and reproduction.

 

 

33. You want to study divergence of populations, and you need to maximize the rate of divergence in order to see results within the period of your grant funding. You have complete ability to capture individuals from the population and you have access to a wide variety of environments. You will form a new population by taking some individuals from a source population and isolating them so the two populations cannot interbreed. What combination of characteristics would maximize your chance of seeing divergence in this study? Why?

 

 

Main Points:

1.    What kind of species to choose to promote change fast relative to our human perspective:

a.    Produces many offspring

b.    short generation time.

2.    Choose a small subset of the population - This allows for small population size ->  genetic drift will have more effect

3.    Chosen subset should have an extreme value of a particular trait. Small subset of the gene pool that codes for subset of the possible phenotypes.

4.    Place the subset in conditions/environment that will enhance the selective advantage of that extreme trait. Must be very different from the original habitat.

 

 

SECTION IV - Extra Credit Question (3 Points) – What was the main point of the Laurie Lebo talk about the Dover Trial? Answer this with a sentence or two that shows me you were there.

 

The role of objective journalism, etc. If I failed to give you sufficient credit and you were at the talk, come see me.