Practice Exam 2 2006

Name________________________________________ Section _______________________

Part I. Fill in the blank with the corresponding letter (9 points)

1. Grifith
2. Reverse
3. Semiconservative
4. Okazaki
5. Transformation
6. Watson and Crick
7. Lagging strand
8. Meselson and Stahl
9. Gene conversion
10. Bacteriophage

1. _____ ____ discovered the double helix structure of DNA

2. ____ _____ demonstrated bacterial transformation of R cells into S cells.

3. DNA’s ___ ____ is synthesized discontinuously as short segments known as__ ____ fragments.

4. In replication, each parental DNA strand directs the synthesis of a new partner strand. This is known as_ ____ replication.

5. ____ used DNA labeled with ¹⁴N and ¹⁵N

6. A _ __ is a virus that infects bacteria

7. An event that restores the wildtype phenotype is called a ________ mutation.

8. ___ is a deviation from the 2:2 segregation ration of parental alleles.

Part II. Short answer

1. If 10% of nucleotide bases in mouse DNA are C, what percentage are A? what percentage are T and what percentage are G? (3 points)

14. You might find this useful: R = h²S

A. In the class example we found that the heritability based on father-daughter relation was much greater than that of mother-daughter relation, for the trait height. Would you use the father’s height or the mother’s height to predict the adult height of your newly born niece? (2 pts)

B. Which combination of parameters would result in the greatest change in a trait across generations (2 pts):

i. strong selection, high heritability

ii. strong selection, low heritability

iii. weak selection, high heritability

iv. weak selection, low heritability

C. A heritability of 0.8 for height indicates

i. what variables are contributing to height variation in the population? (2 pts)

ii. and in what relative proportions? (2 pts)

15. PU is a particularly obnoxious disease, resulting in the emission of highly noxious body odor. The expression of this disease is due to a genetic disorder associated with a recessive mutation and is expressed only in homozygous recessive individual. If 1/1,000,000 or 1 in a million individuals is born with this disease,

A. What is the frequency of the wild type dominant allele in the population (2 pts)? Show all work.

B. What is the frequency of carriers in the population? (2 pts) Show all work.

16. Flower color in the plant Lupinus terpensis is controlled by one locus, two alleles. In Maryland you find large populations of this plant (many thousands of individuals), which have blue flowers (AA), pink flowers (Aa) and white flowers (aa). However, you find small populations found on the numerous islands in the Cheasapeake Bay. These populations are almost always of one color, either blue or white, though the color differs between islands. Provide an explanation why you see only one color on each of the islands, and why you never see pink flowers on the islands (4 pts).

9. Differentiate Phenotype from Genotype (4 pts). Be sure to list those factor(s) that contribute to a phenotype.

14. When artificial selection is imposed on a population, after a number of generations, phenotypes are observed that are more extreme than the phenotypes in the original population. This appears counter to the expectation of mendelian genetics where the extremes are governed by the appearance of either of the alternative homozygotes (AA or aa). What 3 factors can account for selection resulting in phenotypes more extreme than found in the original population and are compatible with both natural selection and mendelian genetics. 6 pts.

15. You might find this useful: R = h²S

A. You are a breeder, trying to breed for decreased size of chickens raised in xeric (dry) conditions, e.g., Sahel in Africa. You measure the heritability of size in conditions simulating these extreme dry conditions and quantify a heritability of 0.5. Size among your chickens ranges from 0.5-2.5 kilos. The mean of the population before selection is 2 kilos, and the mean of the chickens that you allow to breed to produce the next generation is 1 kilo.

i. What is S or the selection coefficient that you, the breeder have exerted on the population? (2 pts)

ii. What is the predicted mean weight of chickens in the next generation? (2 pts)

16. The genotypes SS, Ss and ss are associated with the expression of sickle-cell anemia, Ss are carrier and ss individuals express the disease. You blood type 100 infants in a particular village of West Africa and find 100 individuals of each genotype. You come back 20 years later and observe that of the 100 SS individuals, 10 have died from malaria, of the 100 Ss individuals, all are living, and 50 of the ss individuals have died from complications associated with the sickle-cell trait. For this population:

What is the fitness of each genotype, SS, Ss, ss (3 pts):

What is the selection coefficient associated with each genotype (3 pts)

What is the mean fitness of the population (3 pts)

And what is the equilibrium frequency of the big S allele that you predict, NOTE that the frequency of the big S allele corresponds to p (3 pts)?

2. In the above replicating molecule of prokaryotic DNA indicate a): polarity of all the strands, b) leading and lagging srands, c) DNA polymerase III, d) ligase, f) okazaki fragments, g) RNA primers. (8 pts)

BSCI 222 Quiz # 5

Name________________________________________ Section _______________________

1) In a population of rainforest frogs individuals with a “A” allele have spotted skin whereas individuals that have ‘aa’ genotypes have no spots. Scientist have genotyped the population and have obtained the following proportions of genotypes: 0.60 AA (Spotted) 0.20 Aa (Spotted) 0.20 aa (no spots)

a) What are the allele frequencies for “A” and “a” in this population?.

b) How many individuals of each phenotype do you expect to see in 2000 viable offspring after one generation of random mating (assume HW)?

2) Why is it difficult to eliminate recessive deleterious alleles by natural selection? (6 pts)

Formulas:

F(W)= 2*# of WW + # Ww p²+ 2pq + q²= 1 S= 1-W

2* N

(6 pts) In a certain population of humans, 96% are normal and 4% have wizarding capabilities. If wizarding capabilities are determined by a single gene “W” with complete dominance, what are the allele frequencies for the wizard allele (w) and the normal allele (W)?

w =

W =

(9 pts) If this population has 500 individuals, how many individuals have each of the following genotypes (assuming Hardy Weinberg equilibrium)?

WW =

Ww =

ww =

(2 pts) In this population, individuals with wizarding abilities are burned at the stake before they can reproduce (prejudice knows no bounds). What is the selection against wizards in this population?

(3 pts) In another population, wizarding has polygenic inheritance with a heritability of 0.5. Magical ability ranges in strength from 0 to 20 units (tested as a child, similar to IQ). Among wizards, average magical ability in one generation is 10 units and in the following generation is 9 units. What is the selection differential between the two generations?

(3 pts) Analysis of wily coyote DNA finds that 22% of its DNA is composed of cytosine. What are the percentages of the other bases in the coyote genome?

A = ____ G = _____ T = _____

(14 pts) Use the following terms to fill in the blanks below:

Hydrogen bonds Phosphodiester bonds Purine Pyrimidine

Adenine Thymine Cytosine Guanine Ligase

DNA Polymerase Topoisomerase Lagging Leading

A. ___________________ bases have two cyclic elements in their chemical structure.

B. ___________________ is an enzyme that connects Okazaki fragments on the _______________ strand of a newly synthesized DNA by creating __________________ between the fragments.

C. Complementary base pairing is strongest between _______________ and _______________ because it involves three ______________________.

(2 pts) What is the difference between conservative and semi-conservative replication?

(1 pt) Is DNA replication conservative or semi-conservative?

2) Assume each of the following diagrams represents double stranded DNA. Total = 9 pts.

Complete the first to show DNA replication. Include and label: leading strands, lagging strands, origin of replication. Be sure to note the polarity of the strands in terms of the 5’ and 3’ direction.

Complete the second to show transcription. Include and/or label: the nascent RNA strand, the template strand and the RNA-like strand. Be sure to note the polarity of the strands in terms of the 5’ and 3’ direction.

5. The Watson-Crick model of the hereditary molecule was based on a number of key observations made by other research groups. Briefly describe these key findings in terms of i) the primary constituents of the molecule (i.e., was it protein), ii) the composition of the molecule (in terms of proportions of particular components) and iii) the structure (shape) of the molecule. Total = 6 pts.

6. Meselson and Stahl grew E. coli in ¹⁵N medium for many generations, and then transferred to ¹⁴N medium for one generation (total = 6 pts).

What fraction of DNA banded at an intermediate density, following CsCl centrifugation, after one generation growth on the ¹⁴N medium (3 pts)?

What fraction of DNA banded at an intermediate density after

one additional round of replication on ¹⁴N medium (1 pt)?

two additional rounds of replication on ¹⁴N medium (1 pt)?

three additional rounds of replication on ¹⁴N medium (1 pt)?

7. If 18% of the yeast genome is cytosine, what is the percentage of the other nucleotides? (3 points)

1) In a population that has 2 alleles for a given gene:

p + q = _____? (2 pts)

If we assume the population is in Hardy-Weinberg equilibrium, then we apply the following equation:

p² + 2pq + q² = ____? (2 pts)

2) In a population of flowers, flower inclination is controlled by 2 incompletely dominant alleles, F and f. Upright flowers are dominant to pendant (hanging) flowers, and heterozygote flowers are held horizontally. If there are 20 upright flowers, 20 horizontal flowers, and 20 pendant flowers in a population:

What are the genotypic frequencies?(3 pts):

What are the allelic (allele) frequencies?(4 pts):

If the population was in H-W equilibrium, what would the genotypic frequencies be?(3 pts):

3) If a given phenotype has a fitness of 1, the selection against that phenotype is equal to (2 pts):

a) 1

b) .5

c) 0

4) Animal breeders use the equation R=h²S.

If h² is equal to 1, and S (strength of selection) is equal to 10, what is the response to selection? (2 pts)

If h² is equal to zero (there is no heritability), and the S is equal to 10, what is the response to selection? (2 pts)

1) DNA replication is: (3 pts)

a) conservative

b) dispersive

c) semiconservative

d) liberal

2) DNA contains ______ different base nucleotides (2 pts).

How many are purines?________(2 pts)

How many are pyrimidines?________(2 pts)

4) You have the following strand of DNA: 5’ GATTACA 3’

What strand would be complementary to this?(4 pts) (Remember that DNA is anti-parallel)

a) 3’ GATTACA 5’

b) 3’ CTAATGT 5’

c) 5’ GATTACA 3’

d) 5’ CTAATGT 3’

5) The viruses in Avery’s experiments“injected” ______ into host cells (3 pts)

a) DNA

b) proteins

c) RNA

6) The differential correction of mismatches in the heteroduplex region of homologus chromosomes can result in(4 pts):

a) supercoiling

b) gene conversion

c) mutation