ZOOL/BOT 3333

The answers to the practice exam are found here, but please work the practice exam first!

A. True/False and multiple choice questions (2 points each). Please fill in your answers on the scantron sheets provided. For true/false questions, please indicate whether a statement is true (1) or false (2), or, for multiple choice questions, circle the letter representing the single best choice. If a question seems ambiguous to you, please raise your hand and I will try to clarify the source of ambiguity.

1. Suppose that the DNA from a certain species of bacteria was shown to contain 28% guanine. The amount of thymine found in the DNA would be:
   a) 22%; b) 25%; c) 28%; d) 32%; e) none of the above
2. If one strand of B form DNA has a base sequence of 5'-CGGTAGAC-3', the base sequence of the complementary strand would be:
   a) 5'-CAGATGGC-3'; b) 5'-GCCATCTG-3'; c) 5'-CGGTAGAC-3'; d) 5'-GTCTACCG-3'; e) none of the above.
3. A 40 year old woman gives birth to a son with Down Syndrome. On chromosomal analysis, the child is found to be 47,+21. The number of Barr bodies found in an interphase nucleus in this individual would be:
   a) zero; b) one; c) two; d) three; e) none of the above.
4. Recessive genes a, b, c, d, e and f are closely linked in a chromosome, but their order is unknown. Three deletions in the region are examined. One deletion phenotypically uncovers a, d, and e; another uncovers c, d, and f; and the third uncovers b and c. The relative gene order is:
   a) adefcb; b) eadfcb; c) aedfcb; d) aedcfb; e) either of two possible orders can be assigned on the basis of this data.
5. A pair of transduction studies indicates that the cys locus is cotransduced with the arg locus 45% of the time and with the trp locus 3% of the time. Another pair of trandcuction studies indicates that the trp locus is cotransduced with cys 4% of the time and with arg 0% of the time. The relative order of this linkage group is
   a) cys-trp-arg; b) cys-arg-trp; c) arg-cys-trp; d) none of the above.
6. True or false: The above data indicate that the cys locus is closer to the trp locus than the arg locus.
   
7. The diploid chromosome number of an organism is 10. How many chromosomes would be expected in a nullisomic?
   a) 5; b) 8; c) 9; d) 11; e) none of the above.
8. A tetraploid autopolyploid is derived from a diploid species that contains six pairs of chromosomes. This tetraploid will have how many linkage groups?
   a) 2; b) 4; c) 6; d) 12; e) none of the above.
9. Abyssinian oat (Avena abyssinica) appears to be a tetraploid with 28 chromosomes. The common cultivated oat (Avena sativa) appears to be a hexaploid in this same series. The number of chromosomes present in the gamete cells of the common cultivated oat will be:
   a) 7; b) 14; c) 21; d) 28; e) 42.
10. True or false. During chromosome replication in mammals, replication proceeds bidirectionally from a single origin of replication, located at the centromere.
    

Questions 11-12 refer to the following figure, which represents an example of an E. coli replication fork. Synthesis is proceeding in the direction of the arrows:

11. True or false: At site 1 in the figure, the polymerized DNA chain will end in a 5' phosphate group.
12. At site 3 in the figure, the base-paired molecule which is first formed at the replication fork is:
    a) a DNA molecule synthesized in the 3' to 5' direction; b) an RNA molecule synthesized in the 3' to 5' direction; c) a DNA molecule synthesized in the 5' to 3' direction; d) an RNA molecule synthesized in the 5' to 3' direction; e) none of the above.
13. True or false: Both DNA polymerases I and III contain a nuclease activity which can degrade DNA in the 3' to 5' direction.
    
14. F factors: a) are episomes; b) mediate conjugation; c) carry their own origin of replication; d) all of the above; e) none of the above.
15. True or false. Although normal female Drosophila are XX in karyotype, the genes located on only one of the two X chromosomes will be expressed in any given cell.
    
16. The most easily recognized characteristic of an inversion heterozygote in plants is:
    a) semisterility; b) gigantism; c) a cross-shaped chromosome configuration during meiosis; d) pseudodominance; e) none of the above.
17. True or false. You would expect Okazaki fragments to be completely degraded into individual deoxyribonucleotides after extensive treatment with DNAse.
    
18. Mammalian Y chromosomes:
    a) are largely heterochromatic; b) can pair with the X chromosome during meiotic prophase I; c) contain homology at the DNA level with a region of the X chromosome; d) all of the above; e) none of the above.
19. Which of the following individuals was responsible for the statement, "It has not escaped our notice the specific pairing we have proposed immediately suggests a possible copying mechanism for the genetic material":
    a) Harry Angstrom; b) Watson and Holmes; c) Professor Moriarty; d) Avery Fischer Hall; e) none of the above.
20. You are trying to locate an enzyme-producing gene in Drosophila, which you know is located on the second chromosome. You have five strains with deletions for different regions of the second chromosome ("/" indicates a deleted region):
    

Each of the chromosomes is lethal when homozygous and is maintained with a balancer chromosome carrying multiple inversions, a recessive lethal gene, and a dominant marker gene which produces an abnormal wing phenotype. You cross each of the 5 deletion chromosome strains with wild type flies and measure the amount of enzyme in extracts derived from the F1 progeny which have a wild-type wing phenotype. The results appear in the table below:

Strain crossed

a

b

c

d

e

Percent of wild-type enzyme in extracts

98

47

52

49

100

On the basis of the above information, the gene of interest can be most accurately mapped:
a) between bands 1 and 2; b) close to band 2; c) between bands 2 and 4; d) close to band 4; e) between bands 1 and 6.

B. Match and Identify (2 points each). Please match the following terms in part I with the appropriate definitions or specific examples given in part II. For each term, provide the single best answer; no term in part II should be used more than once. Please note that two circles must be filled for each answer.

part I.

21-2. monoploid
23-4. philadelphia chromosome
25-6. monosomy
27-8. bilateral retinoblastoma
29-30. plaque
31-2. pilli
33-4. facultative heterochromatin
34-5. merozygote
37-8. lysogeny
39-40. semi-conservative replication

part II.

aa) associated with chromosome 13 deletions
bb) male honeybees
cc) temperate phage
dd) partial diploid
ee) "male" E. coli
ab) mechanism identified by x-ray crystallography
ac) chromocenter
ad) result of bacteriolysis
ae) reciprocal translocation
ba) cri du chat Syndrome
bc) Turner Syndrome
bc) a result of X inactivation in mammals
bd) used by Avery to show DNA is transforming principle
be) demonstrated through use of CsCl density-gradient centrifugation

C. Short Problems (15 points). Please answer the following problems. Be sure to show all work (eg. calculations); partial credit can only be assigned on the basis of work shown.

1. ( 7 points). Mr. and Mrs. Denton have been trying for several years to have a child. They have experienced a series of miscarriages, and last year they had a child with multiple congenital defects. The child died within days of birth. The birth of this child prompted the Denton's physician to order a chromosome study of parents and child. The results of the study are shown in the figure below. Chromosome banding was done, and all chromosomes were normal in these individuals except some copies of number 6 and number 12. The chromosome complements of mother, father and child are shown in the figure, with chromosome 6 being the larger pair:

a) Does either parent have an abnormal karyotype? If so, which, and what is the nature of the abnormality?
b) How did the child's karyotype arise?
c) Why is the child phenotypically defective?
d) What can this couple expect to occur in subsequent conceptions?
e) What medical help, information, or counseling, if any, can be offered to them?

2. (8 points) A conjugation experiment is performed to map the location of three genes involved in the ability to synthesize three amino acids, histidine (His), tryptophan (Trp) and leucine (Leu). An Hfr strain with genotype met-his+leu+trp+ is mated with a met+his-leu-trp- recipient. The met marker, which (confers the ability to synthesize the amino acid methionine) is known to be transferred very late. After a short mating the cells are broken apart and plated on four different growth media. The amino acids PRESENT in the growth medium and the number of colonies observed on each are the following:

His, Trp: 250
His, Leu: 50
Leu, Trp: 500
His only: 10

a) True or false: The 500 colonies observed on the Leu, Trp media can now serve as donor cells in subsequent conjugation experiments.
b) What is the order of injection of the genes?
c) What is the purpose of the met- mutation in this experiment?
d) Why is the number of colonies so small for the His-only selection experiment?
e) Suppose you were to select for cells on media supplemented only with Leu. Would you expect the frequency of such exconjugants to be at higher or lower frequency than those observed above? Why?