Evolution 322 midterm exam_answers

1.What is the difference between homology and homoplasy? Give an example of each.
Homology is the similarity between species for a particular organ or structure, under a variet of functions and is due to inheritance from a common ancestor. An example is the arm of a human and the flipper of a dolphin.
Homoplasy is the similarity in characters found between different species due to convergent evolution, not common descent. An example is the fins or a shark and a dolphin.
2.Why does AZT work in short term but not in the long run in combating HIV?
AZT initially blocks reverse transcription of HIV by “fooling” the virus into picking it up instead of normal thymidine during transcription. AZT does not have the right structure to allow
transcription to continue adding nucleotides and so replication is stopped. However, over time HIV mutates and some virions are resistant to AZT because they do not mistake it for thymidine, making AZT treatment ineffective. The AZT resistant virions are selected for under pressue of AZT treatment so that soon all virions are resistant.
3.What are the four requirements for natural selection?
1.There is variation among individuals in a population
2.This variation is heritable
3.In every generation some individuals are more successful at survival/reproduction (there are
limited resources).
4.Survival /reproduction are not random, it is tied to the variation among individuals-those
with the most favorable variations are naturally selected.
4.What is an adaptation?
A characteristic that increases fitness of an individual compared to individuals without the trait.
5.Explain the statement “Natural selection is nonrandom, but it is not progressive.”
Natural selection is not random because it chooses (selects) individuals with traits that cause higher levels of fitness relative to others in the population. However, it is not progressive
because it is not forward thinking, it is free on conscious intent, doesn’t lead to some pre-
determined goal or aim towards higher complexity.
6.What is the modern synthesis?
The uniting of Darwin’s theory of natural selection with Mendel’s work on genetics during the 1930’s and 1940’s.
7.What is the difference between a transversion and transition? Which is more common? Why?
Transitions are substitutions between purine and purine or pyrimidine and pyrimidine, while transversions are between purines and pyrimidines. Transitions are more common because they are not caught as frequently due to their less disruptive structural nature.
8.Calculate the frequencies of the + allele(dominant) and the delta32 allele (recessive) using the
following information:
102 individuals total
75 homozygous dominant (+/+)
24 heterozygotes (+/delta32)
3 homozygous recessive (delta32/delta32)
150+24=174 = number of + alleles in the population
6+24=30 = number of delta32 alleles in the population
204 alleles total in the population
174/204=0.853 frequency of +allele
30/204=0.147 frequency of delta32 allele
9.If a population is in Hardy-Weinberg equilibrium, and we start with allele frequencies of 0.6 for
allele Z and 0.4 for z, what will the frequency of homozygous dominant, heterozygotes, and homozygous recessives be in that population?
p2 +2pq+q2 0.62+(2)(0.6)(0.4)+0.42=1
ZZ=0.36, Zz=0.48, zz=0.16
10.What is it called when selection favors heterozygotes? Give a specific example of this and
explain why it occurs.
Overdominance or heterozygote superiority. This occurs when the heterozygote state for a trait has a higher fitness than either the homozygote recessive or dominant states. An example of this is sickle-cell anemia, where SS results in full blown sickle-cell disease and lowers fitness, Ss offers malaria resistance, and ss offers no malaria resistance.
11.Why is mutation alone not a major factor in changing allele frequencies? What else is necessary
for it to have an effect?
Mutation rates are very low and on their own do not drive change in allele frequencies,
However, when coupled with natural selection, mutations can be selected and rapidly change
allele frequencies in a population.
12.Explain the difference between a nonsynonymous and synonymous substitutions. Which would
(most likely) result in a neutral mutation and why? What theory does this fit?
Synonymous mutations don’t result in an change in the amino acid that is coded for, they are
usually at the third bp position. They most likely will result in silent (neutral) mutations. This fits neutral theory. Nonsynonomous mutations change the amino acid being coded for and usually occur at the first or second bp position of a codon.
Essays (You must use proper English and grammar if you want me to read your essays!).
Choose two out of the three (20 points each).
pare and contrast Special Creation with Descent with Modification (Evolution).There are
three main points on which the two disagree. For each point, give an example that supports
Evolution.
Special Creation states:
Species do not change
Each species was created separately
The Earth and life are young
Evolution states:
Species change over time: this is supported by evidence from living species like the soapberry
bug, which changed beak length in response to a new food item (or vestigial organs, fossil
record).
Species derive from common ancestors: homologies, whether morphological or molecular (the genetic code) support a common ancestor (or relationship between species, or development).
The Earth and life are old: Carbon dating and radiometric dating support an old Earth and life.
2.Explain the study of Beak Shape In Galapagos Finches that we talked about in class. What
evidence was there that evolution occurred with respect to the four requirements of natural
selection?
Grant and Grant studied medium ground finches in the Galapagos island pre and post drought.
They found that before the drought, finches had smaller average beak and body sizes than
following the drought. They found support for the four requirement of natural selection,
specifically:
There was variation in the size of beaks in the finch population. Every finch on the island was trapped and measured.
The variation was found to be heretiable. Grant and Grant were able to measure parent and offspring beak sizes and estimate heritability for beak depth, which is also correlated with body size.
During the drought individuals varied in the success at surviving and reproducing. During the drought, food was very limited and most birds died.
The birds that survived were the ones with the biggest beaks who could crack open the only remaining seeds which were very large and unavailable to smaller beaked birds. The average beak size of finches after the drought shifted to a higher average. The survival and reproduction was non-random as only the large beak finches lived and reproduced.
3.State the requirements for a population to be in Hardy-Weinberg Equilibrium. Give a specific
example of a violation for each requirement and how it affects a population for each of the requirements.
The requirements are:
No mutation: Mutations alone do not usually cause a significant change in allele frequencies, but if coupled with selection can drastically alter allele freq. Ex. E. coli populations started from the same strain and kept under selective environments.
No Selection: Selection causes certain phenotypes increase in the population relative to other phenotypes, if this is heretible, it will change genotype frequency. Ex. ADH alleles in fruit flies.
No Migration: Migration introduces or removes alleles from a population and can change
frequencies. Ex. Lake Erie water snakes.
No chance events (infinitely large population size, no genetic drift): Small populations are often subject to genetic drift which can cause fixation of alleles in a population and loss of
heterozygosity. This can also be thought of as sampling error. Ex. Pingelapese people in South Pacific, founder effect.
Mating is random: Non-random mating doesn’t necessarily change allele frequencies, but does change genotype frequencies and increases homozygosity. Ex. Inbreeding in great tits.。