Midterm 2 Exam Key, BIO 115
Evolution and Society

Letter grades for Midterm 2:
Grade                Count
A  145                8
B 110-144            17
C 73-109              28
D  45-70               5
F <45                   7

Answers are given in RED AND UNDERLINE.

A. Multiple Choice Questions (40 points). Each question has one correct answer and is worth 4 points.

1. New genetic variation is now known to be produced

a. at random

b. when it is needed by natural selection

c. by use and disuse of body parts.

d. only in heterozygotes

2. Natural selection

a. acts directly on genotypic variation

b. does not operate on variation that is entirely caused by environmental variation

c. can only occur through the "struggle for existence".

d. works best when each organism adapts to its environment.

3. The forces that are recognized as important in changing gene frequencies are

a. natural selection and non-random mating

b. non-random mating, mutation and migration

c. mutation, migration, natural selection and drift

d. natural selection, mutation, migration, drift and non-random mating.

4. In the sciences, the term materialism refers to the assumption that:

a. natural phenomena (effects) result from causes

b. you must adopt the simplest explanation consistent with all available information

c. only information from observing the natural world can be used to test hypotheses

d. large effects can be explained by slow processes working over a long time

5. Linnaeus' classification of natural objects, including plants and animals, was

a. intended to reveal the works of God

b. based on the utility of species to humans

c. intended to provide evidence in support of the historical truth of evolution

d. assumed that the earth was hundreds of millions of years old

6. Thomas Malthus' 1798 book Essay on the Principle of Population strongly influenced Darwin's ideas about evolution because it:

a. showed that populations always outgrow available food and other resources

b. demonstrated that the earth must be millions of years old

c. explained why traits are inherited

d. proved that some species had gone extinct

7. How do we know that the oldest rocks on earth are about 4 billion years old?

a. That is how long it would take for the salt in the ocean to accumulate

b. Radioisotope dating of rocks

c. Measurements of the size of the solar system require about that age

d. That is how long it would take the earth to cool to its present temperature

8. Why is it believed that when life first evolved genetic information was stored in RNA (ribonucleic acid) instead of DNA (deoxyribonucleic acid), as it is today?

a. RNA is more chemically stable than DNA

b. All viruses store genetic information in RNA instead of DNA

c. RNA can both store information and act as a catalyst in chemical reactions, making it easier to explain the origin of life

d. The earliest fossil cells have genes composed of RNA

9. In the book The Pony Fish's Glow, George Williams discusses eusocial insects (like honeybees), in which worker insects do not reproduce. This would seem to contradict the idea of natural selection. Williams suggests that the nonreproductive workers are produced by

a. the struggle for existence and therefore survival of these workers.

b. since natural selection is on the success of the entire colony as a sort of superorganism.

c. males instead of females.

d. only seem to be nonreproductive because they are low in the dominance hierarchy.


10. Why is the evolution of the amniote egg so important in the history of land vertebrates (tetrapods)?

a. It was important for the diversification of the birds

b. It allowed them to reproduce fully independent of water.

c. It allowed fish to give rise to amphibians

d. It floats in water, preventing tetrapod embryos from drowning


Section B. Matching: write the name of the term next to the best description of the term. (3 points per correct match, 18 points total)

A. Anthrax

B. Mad Cow Disease


D. Linnaeus

E. Thomas Hunt Morgan

F. Gregor Johann Mendel

__D__ invented the latin bionomal nomenclature used to name and classify species.

__E__ developed the use of the fruit fly, Drosophilia melanogaster, for genetics studies and defined mutation as any heritable change in the phenotype.

__C__ caused by a retrovirus that codes for a reverse transcriptase and a protease. These two enzymes are the targets of the drugs used for treatment.

__B__ proposed that it is caused by a prion, which is a misfolded infectious protein.

__A__ caused by a bacterium, most severe when inhaled.

__F__ developed the principle of segregation and the principle of independent assortment.



Section C. Definitions (42 points). Define the following terms. (7 points each)


1. natural selection

The change in genotypes (and phenotypes) of a population that results when at tleast some of the variation in phenotypes is due to genotype. 


2. mutation (definition used by biologist today)

 a change in the hereditary information (typically DNA) of an organism that can be passed on to offspring


3. homozygote

 a diploid genotype in which both alleles are the same (ex. AA, RR, ss)


4. allele

 variant forms of a gene found at one locus (ex. A is an allele, a is another allele, etc.)


5. divergence

the accumulation of genetic differences in two isolated populations of the same species 


6. reproductive isolation

 the establishment and maintenance of reproductive barriers between two populations based on either prezygotic or postzygotic isolating mechanisms


Section D. Short Answer (10 points each, 40 points total)

1. If you discovered two populations of organisms that were geographically separated but very similar in morphology, what would you have to show to conclude they are separate species if you use the biological species definition to decide?

The populations must be reproductively isolated, they must not be exchanging genes and they must be unable to produce fertile offspring 


2. Why in evolutionary terms is it not a good idea to take Cipro for anthrax if you have not been exposed?

 Bacteria in your body will develop immunity to Cipro through natural selection; this immunity can then be acquired by Anthrax or other harmful bacteria


3. Scientists sometimes use the principle of parsimony to decide between hypotheses. What is the principle of parsimony and under what circumstances would it be used?

 Parsimony is used to distunguish between alternate hypotheses when no experiment can exclusively support one hypothesis. The principle says that the simplest hypothesis should be accepted.


4. Why does the knowledge of the transfer of information from DNA to RNA to protein exclude the Lamarckian explanation that evolution happens through use and disuse of a character?

In order for use and disuse to have evolutionary consequence, the effects of use and disuse must be seen in heritable information. Since only DNA is inherited from parent to offspring, and information flow from DNA to protein is one-way, and use and disuse only affects protein expression, the Lamarckian explanation must be wrong. 


Section E. Short Essay. Please answer in the space provided. (20 points each, 60 points total)

1. What is the relationship between genotype and phenotype?

Genotype refers to the genetic information an individual has, while phenotype refers to visible, measurable characteristics. Within an individual, genotype influences but does not fully determine phenotype. The phenotype of an individual influences their reproductive success, which affects the genotype composition of individuals in the next generation.

2. By defining and distinguishing blending inheritance and particulate inheritance, describe the problems blending inheritance creates for natural selection as a mechanism for evolutionary change which particular inheritance does not.

Blending inheritance is a method of inheritance in which the characteristics of the offspring are determined by averaging the characteristics of the parents. Particulate inheritance is a method of inheritance in which characteristics of the offspring are determined by discrete inheritable particles which may or may not be expressed in the parents that carry them. Blending inheritance reduces the variation in a population every generation. Natural selection requires this variation in order to operate. If the variation was not replaced at an impossibly high rate, natural selection would have no variation to work on.


3. Below is a cladogram for five species and showing four characters (A-D). Answer the questions below the cladogram concerning it.


a. Which character tells us nothing about the relationships of these species?

Circle one: A B C D

b. Indicate on the cladogram where character state C' evolved by drawing a line across the appropriate segment of the tree.

Marked on the cladogram above

c. Why would it be inappropriate to make a genus that included species 1, 3, and 5?

It would not include all of the descendants of the common ancestor of 1, 3 and 5 because 2 and 4 would be omitted. It would therefore violate the convention of a strict heirarchy of taxonomic groups.