Download Key for Practice Exam 4

Key for Practice Exam 4
1. Match the terms with their definition.
a) contains DNA from 2 different sources_ Recombinant DNA molecules ________
b) using recombinant DNA technology to manipulate genes for genetic analysis for developing
products or other applications___ Genetic Engineering ____
c) generates large amounts of pure DNA, which can be manipulated in various ways ___ DNA
cloning ______
d) recognize certain base pair sequences and cut at specific places in those sequences ___
Restriction Enzymes _______
e) what are these base pair sequences, mentioned in the above question, called __ Restriction
Sites ________
f) single stranded overhangs of DNA that will base pair with other single stranded DNA ____
Sticky Ends _______
g) dsDNA molecules in which fragments are ligated; can be introduced into cells, so that the
cells will make more of the recombinant molecule___ Cloning Vector ______
Recombinant DNA molecules, Genetic Engineering, Multiple Cloning Sites, DNA libraries,
Cloning Vector, Restriction Enzymes, Restriction Sites, DNA cloning, Sticky Ends
2. Give the definition of Southern Hybridization and Northern Hybridization. How do they
differ?
Southern hybridization identifies whether a DNA sequence is present on a membrane.
DNA on a membrane (filter paper) is searched using a DNA probe. Northern hybridization
identifies whether a gene is expressed in specific conditions (spatially and temporally).
RNA on a membrane is probed with a DNA probe. They differ because in a Southern Blot
it is DNA on a membrane that is probed, whereas, in a Northern Blot is it RNA on a
membrane that is probed. Also, a Southern blot tells whether a certain DNA sequence is
present or not, and a Northern blot tells if a certain gene is expressed in specific conditions.
3. ColE1 plasmids, commonly used as a vector in recombinant DNA studies, carry genes that
control the production of colicins. Colicins are secreted by E. coli cells and kill other bacteria
lacking the ability to synthesize colicins. Why would these plasmids be particularly useful in
recombinant DNA studies? 4 pts
The genes that control the production of colicins can be used as selectable marker genes in
genetic engineering. Cells that have been transformed with the ColE1 plasmid will kill cells
that have not been transformed. This allows for elimination of cells that are not carrying
recombinant molecules.
4. Huntington’s disease is a rare autosomal dominant trait (lethal in the homozygous dominant
condition). The mutation is an expansion of a nucleotide repeat in the DNA that encodes the
huntingtin protein. Normal individuals have between 6-35 copies of a CAG repeat within the
gene. Affected individuals can have between 36-121 repeats. In addition, as the number of
repeated triplets (CAG) increases, the age of onset in the patient decreases. Individuals with this
disease suffer from progressive neurodegeneration eventually resulting in death.
a. A 20-year old single woman whose father died of Huntington’s disease is concerned about her
risk of eventually developing the disease. What is the probability that she will eventually get
HD, if her mother is phenotypically normal? 3 pts
Hh X hh
50% probability
b. The HD gene has been sequenced and its location on chromosome 4 has been well
characterized. The entire DNA sequence of chromosome 4 has been sequenced. A genetic
screen can definitively determine whether this woman has the HD mutant allele.
i. What components would be needed to PCR amplify the HD alleles from her genome?
We would need the woman’s genomic DNA, primers designed to amplify the HD
alleles, Taq polymerase and dNTPs.
ii. Once the alleles were amplified, how could you compare the size of her alleles to
alleles from other individuals?
Gel electrophoresis could be used to determine the lengths of alleles in the woman
with lengths of alleles from individuals that are normal and those with HD.
iii. If this woman was heterozygous at the HD locus, describe the sizes of the two PCRamplified alleles and how they would compare to amplified alleles from both of her
parents.
Her father is heterozygous. Two alleles would be amplified; one that is short (with the
normal number of repeats) and one that is long. On an agarose gel, these would appear as
two different fragments.
Her mother is homozygous recessive. Only one type of allele will be amplified; one
that is short (with the normal number of repeats). Both alleles appear as one fragment on
the agarose gel.
The amplified fragments from the woman could be compared to those from both
parents. If only one fragment is detected, she is homozygous recessive. If the two
fragments of different length are detected, she is heterozygous.
5. Plasmids are important in biotechnology because they are
A) a vehicle for the insertion of foreign genes into bacteria.
B) recognition sites on recombinant DNA strands.
C) surfaces for protein synthesis in eukaryotic recombinants.
D) surfaces for respiratory processes in bacteria
E) proviruses incorporated into the host DNA.