BIO 112: Principles of Biology II
Review 1 KEY

Spring 2002

Instructions:  This review is worth 120 points (15% of your course grade) and will be due in class Monday, 2/18/01.  No exceptions – late reviews will result in at least a 10% deduction.  You may not consult any references or any other person while working on this review.  Your signature at the bottom of the last page signifies that the work is yours alone and is pledged under the Honor Code.  When you break the seal on the envelope you will have three hours to complete the review!  Please print legibly; I can only grade what I can read!  Alternatively, you may type your answers, but that doesn’t mean you can lengthen your answers.  If you choose to do this, turn in both this review and the typed answers.

For each question or part to a question, limit your answers to the space below each question, unless otherwise specified.  Any part of your answer outside of the space provided will not be graded.

1.      Why might species diversity recover quickly, geologically speaking, after a mass extinction?  Provide two possible reasons, using no more than one sentence for each (10 pts).

Any two of the following, although some answers had significant redundancy between two reasons.

a.       Remaining diversity is available for adaptive radiation.

b.      Many niches are opened up for previously competitively inferior species.

c.       New niches are created as environment changes.

d.      New barriers may create opportunities for allopatric speciation.

2.      Outline the interplay between two mechanisms of microevolution.  How might two mechanisms work together or against each other in affecting the gene pool of a population?  List the two mechanisms you will discuss and briefly describe their actions on populations alone (including whether they are random or nonrandom processes and what assumptions of the H-W equilibrium they violate).  Then outline how they might interact to affect genetic diversity (15 pts).

a.       There are five mechanisms from which to choose (NS, gene flow, mutation, drift, non-random mating).  You receive up to five points per mechanism to list and describe it accurately.

b.      The final five points are for describing the interaction.  I looked for a strong connection between the two mechanisms.  Here are some examples that describe an interaction between mechanisms:

i)        Mutation supplies variation upon which natural selection acts.

ii)       Genetic drift can be reversed or minimized by gene flow coming into a small population.

iii)     Mutation may prevent fixation of an allele that may occur via genetic drift or natural selection (so it counteracts those two mechanisms).

iv)     Selection may prevent genetic drift (may counteract drift), or both may work together to cause fixation of an allele and decrease variation.

v)      Mutations are spread from one population to another via gene flow.

3.      Discuss in detail one type of speciation.  Provide one real example that illustrates that form of speciation event, and list up to two isolating mechanisms that are more likely to be involved in reproductively isolating the species (12 pts).

a.       The description is worth four points; you can choose allopatric, sympatric, or parapatric speciation.

b.      The example must be a real example, not a real hypothetical example, from the text, class, or from your expert knowledge.

c.       Listing two isolating mechanisms is easy – just about any two will do; they may all play a role in all types of speciation, with the following conditions:

i)        Spatial, or geographical, isolation cannot be part of sympatry.

ii)       Obviously, spatial isolation is most likely for allo- and parapatry; it is a necessary condition, although your list may include two other mechanisms.

4.      Provide a one sentence example for each of the following as they relate to evolution, adaptation, and disease (9 pts):

a.       A conflict: an example is any interaction with a pathogen – these conflicts are especially difficult to overcome because the microbial pathogens evolve so much faster than we do and can develop resistance to antibiotics quickly.

b.      A constraint: natural selection can only work with what it’s got to begin with (existing structures/molecules), leading to design constraints.  The vertebrate eye was the most common example.

c.       A trade-off: overdesign of one system upsets the balance or function of another or the entire organism.  Sickle-cell anemia or aging are examples of other types of trade-offs.

5.      What is the importance of genetic variation in natural populations? Give two reasons, using no more than one sentence for each (10 pts).

a.       Provides raw material for natural selection.

b.      Allows species to adapt and respond to environmental change.

c.       Allows for speciation to occur.

d.      Increases chances of survival when catastrophe occurs.

e.       Some of these overlap – you need to have two pretty distinct reasons for full credit.

6.      Using the cladistic method, draw a cladogram representing the evolutionary relationships of the following five species (one being the outgroup).  The traits have been recoded, and a 0 represents the ancestral form of each trait.  There may be more than one correct answer (14 pts). 

The trees can be made in at least four different ways, some making fewer assumptions than others.  See me if you want to discuss your tree.

a.       Circle on your tree (in different color pens, if possible) instances of reversals or convergent evolution.  If you did not have any of either, indicate that here:

Every possibility has at least one instance of convergent evolution or a reversal, depending on how you approached it.

b.      Which species has the most ancestral traits?  The most derived?

The outgroup or D has the most ancestral traits.  A and C are tied for the most derived traits.

7.      What evidence exists that fish-shaped ichthyosaurs were deep divers?  List two main types of evidence that support this view.  Speculate on and list ecological selective factors that may have facilitated the evolution of these types of ichthyosaurs (10 pts).

a.       Acceptable answers include: diet, increased muscle mass, spongy layer in bones, large eyes, eyes with skeletal ring, and streamlined bodies.  For the backbone and caudal fin I gave half-credit (each correct answer netted you 3 points, so these were worth 1.5), since these likely evolved as part of the open ocean lifestyle, but were probably already in place prior to the evolution of the deep diving habit.

b.      Ecological selective factors include: food more dispersed or at lower densities, competition, climate change, predator escape.

8.      Address one of the following (10 pts):

a.       Large-scale environmental change can affect life and its evolution on the entire planet.  Organisms may also affect environmental conditions at a scale greater than that at which they live.  List one example of each of these phenomena during the history of life on Earth. 

Climate change, such as glaciation, sea level change, or rapid temperature shifts, meteors, and continental drift may all cause mass extinctions followed by adaptive radiations.  The two most popular answers for the second half included the evolution of photosynthesis, which radically changed the atmosphere, and humans, who’re very likely causing a mass extinction right now.

b.      Outline how a cline can affect population structure, and how that affects genetic variation of the species.  Compare genetic variation within and among subpopulations, and explain how that might affect evolution of the species. 

Climate or any abiotic factor may vary over a spatial gradient in a consistent manner.  Temperature is an excellent example.  If a species has populations distributed along the cline, and there is either little gene flow among populations or strong selection within populations (or both), then there will likely be large genetic variation between populations and little variation within populations.  Over a long time period, the populations may become reproductively isolated, and speciation may result.

9.      Prokaryotes are incredibly important to the ecology of the biosphere.  Develop a brief argument to support that statement, using specific examples that illustrate prokaryote diversity and ecology (10 pts).

a.       You needed to include at least two examples illustrating both diversity and ecology for full credit.  Many used the nitrogen cycle, which illustrates both, since multiple types of bacteria play a role in cycling nitrogen.  However, another example was required, and that could be anything from their diversity in obtaining nutrition, their role in the evolution of eukaryotes, how some are photosynthesizers and others are decomposers, and how many are symbionts or pathogens.

10.  Discuss one of the following two questions (10 pts):

a.       Select one species concept and define it.  Then outline the pros and cons of using such a concept to define species. 

The Biological, Morphological, and Phylogenetic Species Concept were all possible choices.  You must define the chosen one explicitly.  They all have advantages: for example, the BSC explicitly specifies reproductive isolation, MSC is based on easy and inexpensive techniques, and the PSC specifies evolutionary history and descent from a common ancestor.  They all have disadvantages.  The BSC is not useful for asexually reproducing organisms, and is difficult to apply rigorously when determining the potential for breeding among many populations.  The MSC may be problematic because of homoplasy, but also does not include a genetic inheritance component (reproductive continuity is implied only).  The disadvantages to the PSC are that it is somewhat arbitrary how scientists decide the level of genetic difference between two species, and the data are somewhat difficult to obtain (expensive technique that requires much training).

b.      Distinguish between homology and homoplasy in outline form.  List examples of each to illustrate the distinctions. 

Homology refers to a trait that descends from a common ancestor, even if the trait has evolved to take on a different feature or function in two lineages descended from that ancestor.  The bones that make up bird wings, bat wings, our arms, and forelegs of elephants are all homologous.  Homoplastic traits are similar for some reason other than inheritance from a common ancestor.  Bird wings and bat wings share the same function, but wings evolved from different common ancestors that did not have wings (not the bones, but the wings).  So homoplastic traits refer to convergent evolution and reversals.

11.  A population of Golden Raintree (Koelreuteria paniculata) was sampled for expression of yellow flowers.  Flower color is determined solely by one gene that has a dominant and a recessive allele.  It is discovered that out of 100 trees in the population, the frequency of one allele (Y) is 0.65.  The other allele at the locus studied, a recessive allele (y), codes for white flowers, and was expressed in 10 individuals.  Calculate or derive allele frequency for “y” and observed and expected genotype frequencies for this locus and conclude whether the population is at Hardy-Weinberg Equilibrium (show work – 10 pts).  Use the back for this question only, if needed.

a.       We know Y (p) = 0.65, therefore y (q) = 0.35 (1 point).

b.      To obtain predicted values, simply apply the H-W formula: p² + 2pq + q² = 1.  p² = 0.423,  2pq = 0.455, and q² = 0.123.  Multiply each of these by 100 to obtain the expected number in a population of 100 (3 points).

c.       Since y is recessive, in order for it to be expressed it must be homozygous.  Therefore, yy = 10, or 0.10.  If q = 0.35, and there are 100 x 2 = 200 alleles in the population, then 200 x 0.35 = 70 “y” alleles exist.  Twenty (20) of them are found in the 10 homozygotes, so there must be 70-20 = 50 heterozygotes.  Applying the same logic to the YY homozygotes, if p = 0.65, and there are 100 x 2 = 200 alleles in the population, then 200 x 0.65 = 130 “Y” alleles exist.  130-50 heterozygotes = 80 alleles in 40 homozygote YY individuals.  You can find the 40 also by knowing that [YY + Yy + yy = 100], thus [100 – 10 – 50 = YY], but the former way is better because it provides a check on your math – you can apply the equation [YY + Yy + yy = 100] after you independently determine all three variables and if they don’t add up to 100 then you did something wrong (4 points).

d.      Compare 42 to 40, 46 to 50, and 12 to 10.  You are not expected to calculate chi-square – FYI you can always assume that I will give you formulas for those types of calculations if I want you to calculate that.  All you need to do is visually inspect the numbers and come to a conclusion.  The numbers are fairly close, and are within the realm of sampling error, so it is extremely likely that the population is in H-W equilibrium.  However, you might also suspect that there is some heterozygote advantage or nonrandom mating, but that is less likely based on the numbers (2 points).

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