mutations can be neutral

mutations can be neutral

III. PRACTICE EXAM QUESTIONS

1. Which of the following are true about mutation? Pick the better of the two choices for each statement.
A. mutations can be advantageous T or F
B. mutations can be neutral T or F
C. mutations can be deleterious T or F
D. mutations are a rare occurrence T or F
E. evolution in a population can occur even if mutation doesn’t occur T or F

2. Which of the following are true about evolution? Pick the better of the two choices for each statement.
A. If a person develops immunity to a disease, they have evolved. T or F
B. Microevolution refers to the formation of a new species over long time periods. T or F
C. Evolution occurs at the level of the population. T or F
D. Evolution can occur through neutral mutations. T or F
E. Natural selection can only act on variations currently present in the population. T or F
F. A population can evolve without undergoing natural selection. T or F
G. Traits arise because of a selection pressure. T or F

3. A small cruise ship full of American tourists hits a rock and takes on water during a voyage in the South Pacific. About 150 survivors swim to the nearest island where they form a new society that is isolated from the rest of the world.
A. The population of survivors is likely to have more / less genetic diversity than the population from whence they originally came.
B. The population of survivors is likely to undergo genetic drift / gene flow.
C. This would be an example of population bottleneck / founder effect.

4. A population in Hardy- Weinberg Equilibrium is evolving. True or False
Most populations are in Hardy- Weinberg Equilibrium. True or False

5. What do the terms in the Hardy-Weinberg equations (p + q = 1 and p2 + 2pq + q2 = 1) represent?
p = q =
p2 = q2=
2pq =
6. Did you know that many antibiotic drugs have been developed to combat bacterial infections, and after each new drug has been introduced, bacteria resistant to that drug have been found within a decade? Use your knowledge of evolution to explain how drug resistant bacteria arise.

7. Write a short paragraph to explain this scenario. Use the words variation, selection pressure, heritability, and time. Most living species of lily (plant) have petals. How would biologists explain how a species of lily without petals evolved from an ancestral species of lily that had petals?

8. Which statement is not an assumption of the Hardy-Weinburg law?
A. The allelic frequencies (p and q) are equal.
B. The population is randomly mating.
C. The population is large
D.Natural selection has no effect
9. In cats, all-white color is dominant over not all-white. In a population of 100 cats, 19 are all-white cats. Assuming that the population is in Hardy-Weinburg equilibrium, what is the frequency of the all-white allele in this population?

10. Which of the following statements is an example of genetic drift?
A. Allele “g” for fat production increases in a small population because birds with more body fat have higher survivorship in a harsh winter.
B. Random mutation increases the frequency of allele “A” in one population but not in another
C. c)Allele “R” reaches a frequency of 1.0 because individuals with genotype “rr” are sterile.
D. d Allele “m” is lost when a virus kills all but a few individuals and just by chance none of the survivors possesses the allele “m”.

11. Albinism is a rare genetically inherited trait that is only expressed in the phenotype of homozygous recessive individuals (aa). The most characteristic symptom is a marked deficiency in the skin and hair pigment melanin. This condition can occur among any human group as well as among other animal species. The average human frequency of albinism in North America is only about 1 in 20,000. Calculate the frequency of heterozygous individuals in North America. (from http://anthro.palomar.edu/synthetic/sample.htm )

12. In another study of human blood groups, it was found that among a population of 400 individuals,230 were Rh+ and 170 were Rh-.. Assuming that this trait (i.e., being Rh+) is controlled by a dominant allele (D), calculate the allele frequencies of D and d. How many of the Rh+ individuals would be expected to be heterozygous?

13. The American Toad (Bufo americanus) mates at the beginning of summer and the Fowler’s Toad (Bufo fowleri) mates at the end of summer. What is the most likely mechanism that keeps these species distinct? _____________________
14. Two different species of bonobo monkeys try mating but fertilization does not occur. What two possible mechanisms keep these species distinct? _____________________
15. A male Red-capped Manakin (Pipra mentalis) performs a dance for a crowd of female Red-headed Manakins (Pipra rubrocapilla) to impress the ladies, but sadly none appear interested. What is the mechanism that keeps these species distinct? _____________________Here is a cool video! http://www.youtube.com/watch?v=i-wtO7pjJKk
16. The process of a new species arising within the range of the original populations is termed:
A. convergent evolution C. allopatric speciation E. Hybridization
B. sympatric speciation D. polyploidy

17. A pregnant female rat is transported by an ocean liner to a new continent. Eventually her descendents are considered to be a different species than the population she came from.
A. allopatric speciation B. sympatric speciation

18. What type of variation in an organism is passed to its offspring?
A. Any behaviors that were learned during the organism’s lifetime.
B. Only characteristics that were beneficial during the organism’s lifetime.
C. All characteristics that were genetically determined.
D. Any characteristics that were positively influenced by the environment during the organism’s lifetime.

V. HOMEWORK ASSIGNMENT 1

NAME _________________________________ Student ID ________________________________ POD _________
General Biology II (BIOL 2061) – Spring 2011 – Due January 31th in Class
You can work on this assignment with anyone in class, but each person must turn in an original, typed paper. Copying another student’s work (even for one question) will result in a zero for the entire assignment. You can discuss questions using the class blog too. This will help you study for the quiz and exam, so do your best work! Try not to use more than the space provided to answer each question. Each question is worth 10 points out of 100. Type your answers.

INTRODUCTION
The rock pocket mouse, Chaetodipus intermedius, is a small, nocturnal animal found in the deserts of the southwestern United States. Most rock pocket mice have a sandy, light-colored coat that enables them to blend in with the light color of the desert rocks and sand on which they live. However, populations of primarily dark-colored rock pocket mice have been found living in areas where the ground is covered in a dark rock called basalt. The basalt formed from cooling lava flows thousands of years ago. Scientists have collected data from a population of primarily dark-colored mice living in an area of basalt called the Pinacate lava flow in Arizona, as well as from a nearby light-colored population. Researchers analyzed the data from these two populations in search of the genetic mutation responsible for the dark color. Their analysis led to the discovery of a mutation in the Mc1r gene, which is involved in coat-color determination.
PART 1 – PROCEDURE
A. Read the following excerpt from an article published in the Smithsonian magazine by Dr. Sean Carroll, a leading evolutionary biologist and Howard Hughes Medical Institute investigator:
“One of the most widespread phenomena in the animal kingdom is the occurrence of darkly pigmented varieties within species. All sorts of moths, beetles, butterflies, snakes, lizards and birds have forms that are all or mostly black…All of these so-called “melanic” forms result from increased production of the pigment melanin in the skin, fur, scales, or feathers. Melanic pigmentation can serve many roles. Melanin protects us and other animals from the ultraviolet rays of the sun, it can help animals in colder climates or higher altitudes warm their bodies more quickly, and black pigment does conceal some animals from predators.
In the deserts of the southwestern United States, for instance, there are outcrops of very dark rocks that were produced by lava flows over the past two million years. Among these rocks lives the rock pocket mouse, which occurs in dark black and a light, sandy color. Naturalists in the 1930’s observed that mice found on the lava rocks were typically melanic, while those on the surrounding sand-colored granite rocks were usually light-colored. This color-matching between fur color and habitat background appears to be an adaptation against predators, particularly owls. Mice that are color-matched to their surroundings have a survival advantage over mismatched mice in each of the two habitats…
The gene involved in the origin of melanism in (some) rock pocket mice is called melanocortin receptor 1, or MC1R for short. That is not a very interesting nugget of information, until I tell you that the melanic forms of jaguars, snow geese, arctic fox, fairy wrens, banaquits, golden lion tamarins, arctic skua, two kinds of lizards, and of domestic cows, sheep, and chickens are caused by mutations in this very same gene. In some species, precisely the same mutations have occurred independently in the origin of their dark forms. These discoveries reveal that the evolution of melanism is not some incredibly rare accident, but a common, repeatable process. Evolution can and does repeat itself.” (Carroll, S. Evolution in Black and White. Smithsonian.com, February 10, 2009).
B. Watch the short film titled The Making of the Fittest: Natural Selection and Adaptation (this is posted on Bboard if you want to watch it again).
C. Using a genetic code chart, such as the one here (or one in any biology text) and the mRNA codons provided in the table below, fill in the appropriate amino acids in the boxes left blank. The columns from the Pinacate light-colored and dark-colored rock pocket mouse populations studied in the film have been filled in for you.

Mc1r Gene Missense Mutation Amino Acid Positions Pinacate Light Mouse Population
Pinacate Dark Mouse Population
Kenzin Dark Mouse Population
Armendaris Dark Mouse Population Carizzozo Dark Mouse Population
018 mRNA CGC UGC CGC CGC CGC
Amino acid Arg Cys
109 mRNA CGG UGG CGG CGG CGG
Amino acid Arg Trp
160 mRNA CGG UGG CGG CGG CGG
Amino acid Arg Trp
223 mRNA CAA CAC CAA CAA CAA
Amino acid Gln His

D. Answer the questions below.
1. Most rock pocket mouse populations have sandy-colored fur, which is consistent with the light color of the desert rocks and sand on which they live. On the other hand, dark coat-colored rock pocket mouse populations have been found living on black, basaltic rock formations caused by geologic lava flows. What is the best explanation for these facts?

2. The Mc1r gene encodes a protein called the melanocortin 1 receptor (MC1R). This receptor plays a role in the coat color of the rock pocket mouse. When the normal Mc1r gene is present, melanocytes, which are melanin-producing skin cells, decrease the production of the dark-colored pigment called eumelanin and increase the production of the light-colored pigment, pheomelanin. The mutated version of the Mc1r gene results in an increase in the production of eumelanin by melanocytes, resulting in the dark coat-color phenotype.
a. In the data provided in Step 3 of the Procedure, the MC1R protein in the dark rock pocket mouse population from the Pinacate lava flow contains how many mutations?
b. Compare the amino acid data of dark-colored mice from the other three populations to that of the wild-type (light-colored) mice in the Pinacate region. What do you notice?
c. Use the information in the passage on page 1 to explain the evolutionary significance of MC1R protein variations in the different mouse populations.
3. Charles Darwin proposed the mechanism of evolution called natural selection. Explain the theory of natural selection.
4. Natural selection is just one mechanism of evolution. What are the others? Use your textbook or other Internet resources if necessary.
5. If two of the lava flows in New Mexico were in close proximity to each other and included spans of rocky outcrops between them, what would be a possible mechanism, other than new mutations, to drive the decrease in the light coat- colored gene frequency and the increase in the dark coat-colored gene frequency in these rock pocket mouse populations? Explain your answer.
PART 2 – PROCEDURE
A. Review the principles of Hardy-Weinberg Equilibrium
The genetic definition of evolution is a change to a population’s gene pool. Gene pool is defined as the total number of alleles present in a population at any given point in time. According to the Hardy-Weinberg theorem, a population is in equilibrium (and is therefore not evolving) when all of the following conditions are true:
1. The population is very large and well mixed.
2. There is no migration.
3. There are no mutations.
4. Mating is random.
5. There is no natural selection.
To determine whether a population’s gene pool is changing, we need to be able to calculate allelic frequencies. Suppose, for example, a gene has two alleles, A and a. Each individual has one of three genotypes: AA, Aa, or aa. If the population is in equilibrium, the overall number of A alleles and a alleles in the gene pool will remain constant as will the proportion of the population with each genotype. If allele frequencies or genotype frequencies change over time, then evolution is occurring.
Two equations are used to calculate the frequency of alleles in a population, where?p represents the frequency of the dominant allele and q represents the frequency of the recessive allele:
p + q = 1.0
and
p2 +2pq+q2 =1.0
The first equation says that if there are only two alleles for a gene, one dominant and one recessive, then 100% of the alleles are either dominant (p) or recessive (q).
• The second equation says that 100% of individuals in the population will have one of these genotypes: AA, Aa, and aa. Let’s look at each of these one by one to understand the equation:
• If p represents the frequency of the A allele, then the frequency of the genotype AA will be (p)×(p) or p2.
• If q represents the frequency of the a allele, then the frequency of the genotype aa will be (q)×(q) or q2.
• For heterozygotes, we must allow for either the mother or the father to contribute the dominant and recessive alleles. You can think of it as allowing for both genotypes Aa and aA. So, the frequency of the heterozygous genotype is calculated as 2pq. ?In rock pocket mice, several genes code for fur color. Each of those genes have several possible alleles. That’s why there is a range of fur color from very dark to light. For simplicity, we will work with two alleles at one gene. The allele for dark- colored fur (D) is dominant to the allele for light-colored fur (d). In this scenario, individual rock pocket mice can have one of three genotypes and one of two phenotypes, as summarized in the table below.
Genotype Phenotype
Homozygous dominant DD Dark
Heterozygous Dd Dark
Homozygous recessive dd Light

So, applying Hardy-Weinberg:?p = the frequency of the dominant allele (D)
q = the frequency of the recessive allele (d) p2 = the frequency of DD?2pq = the frequency of Dd?q2 = the frequency of dd
This can also be expressed as: (the frequency of the DD genotype) + (the frequency of the Dd genotype) +(the frequency of the dd genotype) = 1
SAMPLE PROBLEM
In a hypothetical population consisting of 100 rock pocket mice, there are 81 individuals with light, sandy-colored fur. Their genotype is dd. The other 19 individuals are dark colored and have either genotype DD or genotype Dd.
Find p and q for this population and calculate the frequency of heterozygous genotypes in the population. It is easy to calculate q2.
q2 = 81/100 = 0.81 or 81%
Next, calculate q.?q = square root (0.81) = 0.9
Now calculate p using the equation p + q = 1 p + (0.9) = 1?p = 0.1
Now, to calculate the frequency of heterozygous genotypes, we need to calculate 2pq. 2pq = 2(0.1) (0.9) = 2(0.09)?2pq= 0.18

PART B: APPLYING HARDY-WEINBERG TO ROCK POCKET MOUSE FIELD DATA
Dr. Nachman and his colleagues collected rock pocket mice across 35-kilometers of the Arizona Sonoran Desert that included both dark, rocky lava outcrops and light rocky granite areas. Substrate color and coat color frequencies were recorded for each location. Each site was separated from any of the others by at least 8 kilometers. A total of 225 mice were trapped. His data is summarized below:

Collection Site Substrate Color Number of Mice Phenotype – Light Phenotype – Dark
1 Light 6 6 0
2 Light 85 80 5
3 Dark 7 0 7
4 Dark 5 0 5
5 Dark 45 3 42
6 Light 77 34 43

1. Calculate the overall frequencies of light-colored mice and dark-colored mice caught on light-colored substrates. Frequency = (number of mice of one color)/(total number of mice)
Frequency of light-colored mice________ Frequency of dark-colored mice________?
2. Calculate the overall frequencies of light-colored mice and dark mice caught on dark-colored substrates. Frequency = (number of mice of one color)/(total number of mice)
Frequency of light-colored mice________ Frequency of dark-colored mice________?
?3. Using the Hardy-Weinberg equation and data from the table above, determine the number of mice with the DD and Dd genotypes on the rocky, light granite substrate.?
Frequency of mice with DD genotype on light substrate ________
Frequency of mice with dd genotype on light substrate ________
Frequency of mice with Dd genotype on light substrate ________
4. Using the Hardy-Weinberg equation and data from the table above, determine the number of mice with the DD and Dd genotypes on the rocky, dark lava substrate.
Frequency of mice with DD genotype on dark substrate ________
Frequency of mice with dd genotype on dark substrate ________
Frequency of mice with Dd genotype on dark substrate ________
5. Which fur color seems to have the greatest overall selective advantage? Use data collected from both dark-colored and light-colored substrates to support your answer.
6. According to the film, what environmental change gave a selective advantage for one coat color over another?

7. In a separate study, 76 rock pocket mice were collected from four different widely-separated areas of dark lava rock. One collecting site was in Arizona. The other three were in New Mexico. Dr. Nachman and colleagues observed no significant differences in the color of the rocks in the four locations sampled. However, the dark-colored mice from the three New Mexico locations were slightly darker than the dark-colored mice from the Arizona population. The entire Mc1r gene was sequenced in all 76 of the mice collected.
The mutations responsible for the dark fur color in the Arizona mice were absent from the three different populations of New Mexico mice. No Mc1r mutations were associated with dark fur color in the New Mexico populations. These findings suggest that adaptive dark coloration has occurred at least twice in the rock pocket mouse and that these similar phenotypic changes have a different genetic basis. How does this study support the concept that natural selection is not random?
8. To determine if the rock pocket mouse population is evolving, explain why is it necessary to collect fur color frequency data over a period of many years?

 

 

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