Genetics I
Exam 5 Review Sheet
NOTE: These are just some of the important aspects presented for Test #5 that you should
be familiar with. This Review Sheet DOES NOT represent all material that could be
covered on the Exam. This Review Sheet is to help guide you in your preparation for the
Exam. Be sure to fully study your class notes, slides (lectures 20-24), outside readings
(Genetics and the Shape of Dogs, Transgenic Livestock as Drug Factories, Sunlight and
Skin Cancer, A New Genetic Code, and DNA's New Twists (Trends in Genetics), workbook
(pages 241-336-Omit Three Factor Crosses pages 249-262), and text book.
Remember that Exam 5 is taken on the day of your Genetics Final Exam along with the
optional comprehensive replacement test. Consider reviewing the review sheets from the
previous exams to help you study for the optional comprehensive final.
1. What is the definition of a cellular clone? (You also learned about DNA clones).
2. One example discussed in class was somatic cell hybridization fusing human and mouse
cells.
a. What virus allows the human and mouse cells to fuse to create a hybrid cell?
What is the term for the cells when the two cytoplasm fuse? What is the term for
the hybrid cell when the human and mouse nuclei fuse?
b. Once the human and mouse cells are fused, the hybrid cells randomly shed (get
rid of) human chromosomes. Geneticists can easily distinguish between the
mouse and human chromosomes based on staining. Specific DNA markers can
identify what chromosome has a specific sequence present. These markers are
complementary to the DNA sequence and can bind to or “hybridize” to the DNA
and be recognized such as with specific staining or fluorescence. Based on the cell
lines and the media used, this information can be used to determine where certain
genes are located (on which human chromosome).
c. In the example from class, what kind of mutant are the mouse cells (what gene)?
What kind of mutant are the human cells? [Hint: a mutant cell is negative (or
lacks) a certain gene.]
d. Based on the somatic cell hybridization data in your class slides, which
chromosome appears to code for the enzyme thymidine kinase?
3. Define linkage.
4. Define crossing-over. Recall that crossing-over occurs during Meiosis I. Does crossingover occur between sister or non-sister chromatids?
5. Explain the Holliday Model of Crossing Over. Include the following enzymes in your
explanation:
a. Endonuclease, DNA binding and/or DNA unwinding proteins (aka gyrase and
helicase), proteins such as recA, Exonuclease, DNA polymerase, and DNA ligase
6. You perform two-factor crosses between F1 individuals and test-cross parents. Suppose
you obtain the genotypic ratios found below in a, b, and c in the offspring among your
different crosses. Label the ratios as Independent Assortment, Complete Linkage, or
Normal Linkage.
a. 6:1:7:2
b. 1:1:1:1
c. 1:1
7. In a normal linkage situation, which testcross offspring are the in highest percentage: the
parental or the recombinant types? Why? Know how to use this information to
determine the configuration of the F1 parent (aka if the F1 parent was cis or trans).
8. What is the maximum percentage of crossing over between two genes (aka what is the
maximum amount of recombination)?
9. How do you calculate the percentage cross-over/recombination when given the numbers
of each of the genotypes of the offspring resulting from a cross between an F1 parent and
a testcross parent?
10. What is the map unit distance between two genes (aka what does the map unit distance
indicate to a geneticist)?
11. When does the percentage cross over equal the map unit distance?
12. How do you figure out the map unit distance between two genes if the percentage linkage
is over 20%?
13. Be able to place genes in order on a chromosome based on the number of testcross
progeny. For instance, take genes A, B, and D. Perform two-factor crosses first
involving genes A and B, then with genes B and D, and finally A and D. Examine the
percentage cross-overs and determine the map unit distances between the genes.
14. As the distance between two genes increases, there is a tendency for the percent cross
over to increase or decrease (circle one).
15. Does crossing-over occur in male Drosophila melanogaster?
16. Please explain the importance of a three factor cross. Consider double cross-over events.
17. What is the term for “Sudden, heritable changes in genetic material and the processes by
which these changes occur”
18. We went over an example of a mutation involving chromosome 22 and chromosome 9 in
humans. This mutation involved translocation (a type of aberration) where chromosome
22 becomes abnormally shortened which leads to CML (chronic myeloid leukemia).
What is the name of the shortened chromosome 22 that causes this disease?
19. Mutations are usually lethal and recessive. When could a mutation be a good thing?
20. Can mutations occur in any cell type?
21. Describe the difference between spontaneous and induced mutations.
22. What is a mutagen (aka a mutagenic agent)?
23. What is the minimal level of DNA base pair mistakes allowed naturally without causing
problems associated with mutations?
24. List the three examples of ionizing radiation that could cause mutations in DNA.
25. What is an example of non-ionizing radiation that can cause mutations?
26. List examples of chemical mutagens.
27. What else (naturally) has the capability to cause DNA mutations? Hint: It is debatable
whether these are considered living or not.
28. Who in 1927 used x-rays to show that external factors could cause DNA mutations using
Drosophila melanogaster?
29. Low intensity x long time (chronic dosage) = ?
30. What is a point mutation?
31. What is a silent mutation?
32. What is a mis-sense mutation?
33. What is a non-sense mutation?
34. Please describe what happens in deletions and insertions.
35. Are silent mutations, mis-sense mutations, non-sense mutations, and deletions and
insertions all also considered point mutations?
36. What are the three general steps of DNA repair?
37. What occurs during Depurination DNA damage? What nucleotide bases are involved?
What bond is broken?
38. What occurs during deamination? What nucleotide bases are involved?
39. How is depurination damage repaired (recall the three general steps of DNA repair)?
Note the specific enzymes involved in each of the repair steps.
40. How is deamination damage repaired? Hint: The first enzyme is different in
deamination, but then the steps of repair are exactly the same as in depurination DNA
repair.
41. Deamination and depurination events are considered hydrolytic reactions. What
molecule causes the DNA damage?
42. When DNA ligase repairs a phosphodiester bond in the sugar phosphate backbone of
DNA, what molecule is produced?
43. How specifically does UV light affect/damage DNA? How is this DNA damage
repaired?
44. Can DNA replication and transcription proceed if a pyrimidine dimer is formed?
45. A genetic disorder of DNA repair in which the body's normal ability to remove damage
caused by ultraviolet light is deficient. This leads to multiple basaliomas and other skin
malignancies at a young age. In severe cases, it is necessary to avoid sunlight. What is
the name of this genetic disorder?
46. There are the multiple alleles (three or more allelic forms of a gene) present in the
population. How many alleles are present per gene in a somatic cell of an individual
organism in that population?
47. When working with multiple alleles, what formula is used to determine the number of
different genotypes possible? What does the letter “n” represent in the formula?
48. List the two examples of multiple alleles discussion in class.
49. Have a general understanding of the immunology associated with blood types. Why
can’t you give someone with type A blood a blood transfusion using type B blood? What
blood type is the universal donor? What blood type is the universal recipient?
50. What are quantitative traits? List a few examples of quantitative traits.
51. Quantitative traits exhibit continuous variation (as compared to discrete variation which
is a one-or-the-other situation such as “yes” or “no”). What shape does a graph have
when the frequency (percentage) of individuals is plotted on the y axis and the
quantitative traits (phenotypes) are plotted on the x axis?
52. What happens to the graph as the number of additive genes (genes all interacting on the
single trait) increases?
53. What is another term for multiple genes working in conjunction to influence a single
trait?
54. How do you determine the number of genes that interact to control a particular
quantitative trait (aka what is the formula used in quantitative traits)? What does the
letter “n” represent in the formula? Do you set the formula to equal the number of
genotypes or phenotypes present in the population in order to solve for “n”?
55. What is heterosis (aka hybrid vigor)? How do you calculate heterosis?
56. What is heritability? How do you calculate heritability? Distinguish between the
unselected population mean, the selected population mean, and the new population mean.
Recall that the h2 component of the equation is calculated in decimal form (i.e. 33% is
0.33) and the h2 value does NOT need to be squared. h2 is a representation of the value.
57. As selection occurs on a quantitative trait, will the curve become narrower or wider?
58. Give the definition for a population.
59. Define population genetics.
60. What is gene frequency within a population? How can gene frequency be modified in a
population?
61. List the formulas for determining genotypic frequencies and allelic frequencies.
62. Define the ideal of Hardy-Weinberg Law (equilibrium). What are the five assumptions
that must be met in Hardy-Weinberg Law in order for allele frequencies in a population
to remain constant over the generations?
63. Hardy-Weinberg Law utilizes the two equations listed below. Please describe what p and
q represent. What do p2, 2pq, and q2 represent?
a. p + q = 1
b. p2 + 2pq + q2 = 1
64. Know how to determine p and q given the numbers of homozygous recessive individuals
present in a population. Understand that knowing the p and q allele frequencies allows
you to calculate the percent or frequency of individuals of a particular genotype in the
population.
65. Know how to calculate the probability of a gamete carrying a particular gene. Know how
to calculate the probability of particular gametes fusing to form homozygous and
heterozygous individuals in that population.
66. Allele frequencies in a population can be compared between the generations by using the
Chi-square goodness of fit test. What is the formula for the Chi-Square test?
67. Understand how to calculate the expected numbers of individuals of each genotype in the
current population using the formerly known allele frequencies and the current
population size.
68. In a Chi-Square goodness of fit test evaluating Hardy-Weinberg Equilibrium/Law (aka
that the allele frequencies do not change over the generations) what is the null hypothesis
and the alternative hypothesis? What degree of freedom will you use in this particular
test? What is the Chi-Square value in the table at that degree of freedom and at P=0.05?
69. If your calculated Chi-Square value is less than the table Chi-Square value, will you
accept or reject the null hypothesis? If you accept the null hypothesis, what does that
indicate in terms of Hardy-Weinberg Equilibrium/Law?
70. If you wish to select for a particular trait, what three characteristics must the trait possess
in the population?
71. Describe the two main purposes of DNA cloning.
72. Name the two means by which DNA is derived for cloning.
73. If you are using DNA of known character, you could create a cDNA library to enable you
to study parts of the DNA of interest. cDNA is double stranded DNA made from single
stranded mRNA of your DNA or gene(s) of interest. Describe the steps (and enzymes)
involved in creating double stranded DNA from mRNA. What is unique about the
enzyme reverse transcriptase? What enzyme cleaves that final hairpin loop?
74. What kinds of enzymes does the “shotgun approach” use? List an example of this kind of
enzyme.
75. The DNA pieces formed from the shotgun approach may be cloned. The DNA is inserted
into a vector and placed into a host cell. Define vector and host cell. List at least one
example of a vector. List an example of a prokaryotic and a eukaryotic host cell.
76. In order for a DNA fragment to be inserted into a specific vector, should both the DNA
and the vector be cleaved with the same restriction endonuclease? Why or why not?
77. What enzyme forms the covalent linkage between the DNA fragment and the vector’s
DNA (such as a plasmid)? Hint: this enzyme forms the phophodiester bonds on the sugar
phosphate backbone of DNA.
78. What is the polylinker region on a plasmid vector?
79. Define the term “recombinant DNA.”
80. How can recombinant DNA be taken up by a host cell?
81. Not all host cells will take up the recombinant DNA, so we have to select or screen for
cells that have taken up the recombinant DNA (because we aren’t interested in host cells
that don’t contain the DNA of interest). Describe the techniques used to screen if a host
cell has taken up your recombinant DNA. Hint: think about antibiotic resistance, X gal
media, and replica plating and autoradiography.
82. What is the purpose of PCR (Polymerase Chain Reaction)? What happens to the DNA
during the PCR reaction? How is a specific segment of DNA amplified?
83. Name the three main steps in PCR (Polymerase Chain Reaction). This occurs in a
machine called a thermal cycler. It takes about 3 hours to run through 25-30 cycles of
these three steps:
a. _____________ Occurs at 90-95ºC
b. _____________ Occurs at 37-70ºC
c. _____________ Occurs at 70-75ºC
84. What specific polymerase is commonly used for PCR reactions? Why is this polymerase
used for this reaction?
85. Who won the Nobel Prize in 1993 for the use of Taq Polymerase in PCR?
86. What is Real Time PCR?
87. Name the two kinds of gels we discussed that are used in gel electrophoresis? Aka what
are the gels made of? Hint: you make the gel almost exactly like you make Jello-only
you don’t have to refrigerate the gel-it solidifies at room temperature.
88. What kind of liquid needs to be pored over (and submerges) the gel during gel
electrophoresis?
89. Describe how gel electrophoresis works. Do smaller or larger DNA fragments move
through the gel faster? What charge is DNA? So where would you place the cathode
(negative charge) and the anode (positive charge) in relation to a gel with DNA samples
placed in the wells?
90. How are the bands on the gel visualized? What is ethidium bromide? How can you
visualize bands on a gel that has been stained with ethidium bromide?
91. What are the steps of Southern Blotting?
92. What information does restriction mapping and chain termination sequencing give us?
Hint: it is in the name.
93. Describe the restriction mapping technique. What kinds of enzymes are used? How
many tubes will you need? Why?
94. How do you read the DNA sequence on the gel after performing the restriction mapping
technique? Which end of the DNA (5’ or 3’) is at the bottom of the gel? Do you know
the first nucleotide using this technique?
95. Chain termination sequencing uses small amounts of dideoxyriboneucleotide triphosphate
precursors (ddNTPs). Dideoxy means there are two hydroxyl groups (-OH) missing from
the ribose sugar instead of the usual one in DNA (at carbon #2). At which carbon
position (#) is the second hydroxyl group missing? Why would this stop/terminate DNA
synthesis?
96. Chain termination sequencing can use radioactive labeling with four different tubes and
four different lanes on the gel OR it can be done using one tube and one lane on the
electrophoretic gel. How is it possible to use only one tube and lane? What are the
ddNTPs labeled with to make this possible?
97. Why is only a small amount of ddNTPs added to the chain termination sequencing
reaction? Describe the competitive exclusion process.
98. How do you read the DNA sequence on the gel after performing the chain termination
sequencing using radioactive labeling (so you have four lanes on the gel)? Which end of
the DNA (5’ or 3’) is at the bottom of the gel? Are you reading the sequence of your
original DNA strand or its complementary strand off the gel?
99. How do you read the DNA sequence after performing the chain termination sequencing
in a single tube (using fluorescent dyes)? Are the peaks the sequence of the original
DNA strand or its complementary strand sequence?
100. List all of the DNA technologies we discussed that used 32P (radioactive)?