BIOL/PBIO 3333
Genetics
Quiz 4
11/16/13
For the answers to the quiz, click here
Questions 1-4 pertain to the following. A mouse null mutant for a particular enzyme has been
identified by the fact that when heterozygotes for the mutation are crossed, 2/3 of the offspring show ½
of the normal level of enzyme activity. By comparing the protein levels in heterozygotes to wild type
mice on electrophoretic gels, the enzyme protein is identified, eventually leading to the biochemical
isolation of the enzyme protein. A small portion of the sequence of the purified enzyme protein is
determined to be:
Phe-Ser-Glu-Tyr-Met-Ile-Trp-Val-Met-Arg-Tyr-Ala-Gln-Tyr-Met
This information is used to synthesize 21-base oligonucleotides that will be used to screen a cDNA
library by nucleic acid hybridization for the cDNA encoding this particular enzyme.
1. What region of the amino acid sequence above should be used to manufacture an appropriate
nucleotide probe?
a) Phe-Ser-Glu-Tyr-Met-Ile-Trp; b) Met-Ile-Trp-Val-Met-Arg-Tyr; c) Glu-Tyr-Met-Ile-Trp-Val-Met;
d) Met-Arg-Tyr-Ala-Gln-Tyr-Met; e) any of the above would be equally effective.
2. How many different oligonucleotides would be present in the least degenerate probe from this
sequence?
a) 21; b) 48; c) 64; d) 192; e) none of the above.
3. What was the source molecule used to synthesize the cDNA that is present in the library to be
screened?
a) wild-type genomic DNA; b) mutant genomic DNA; c) mRNA from a tissue showing high levels of
enzyme activity; d) mRNA from a mouse that is homozygous mutant for the enzyme; e) protein
purified from an electrophoretic gel.
4. True or false. Although a single stranded degenerate probe encoding the protein sequence indicated
above could be used to screen cDNA libraries, it could not be used for a Northern blot analysis.
7.0 kb
5.3 kb
4.0 kb
3.0 kb
1.7 kb
Questions 5-6 pertain to the above: A large family is segregating an autosomal dominant disease of
late onset (approximately 40 years of age). A genomic DNA sample from each family member is
digested with the restriction enzyme HindIII, run on an electrophoretic gel, and subjected to Southern
blot analysis. The probe used in this instance hybridizes to a DNA fragment which shows
polymorphism for this restriction enzyme. The autoradiogram of this blot is shown above, aligned
with the family pedigree.
5. In the above example, which of the following are likely to be physically linked to the disease gene
allele in individual I-2?
a) the 5.3 kb fragment; b) the 1.7 kb fragment; c) both the 5.3 and 1.7 kb fragments; d) the 7 kb
fragment; e) this polymorphism is not linked to the disease gene.
6. Which of the following most accurately represents the map distance between the disease gene and
the marker (probe DNA) locus?
a) 0.02 map units; b) 1 map unit; c) 7.7 map units; d) 22 map units; e) the restriction sites and disease
gene show independent assortment, so this can’t be calculated.
Consider the gel at the right, derived from a sequencing reaction based on the Sanger chain termination
method.
A
7. The sequence of the TEMPLATE STRAND
would be:
a) 5'-ACGTGCACGTGC-3';
b) 5'-CGTGCACGTGCA-3';
c) 5'- TGCACGTGCACG-3';
d) 5'-GCACGTGCACGT-3';
e) 5'-GCTAGCGCTAGC-3'.
G
C
T
8. True or false. Of the four DNA polymerase reactions used for Sanger DNA sequencing, only one
contains deoxyadenosine triphosphate.
Questions 9 and 10 pertain to the following. Six independently derived mutants are recovered in
Neurospora that are all able to grow on compound Z. The mutants are then grown on minimal media
supplemented with one of 6 chemicals all known to be precursors to compound Z. A summary of the
ability of the mutants to grow on media containing these chemicals is indicated below, where a “+” sign
indicates growth and a “-” sign indicates no growth.
Mutant
number
1
2
3
4
5
6
Q
R
Chemical Compounds
S
T
U
V
W
+
+
+
+
+
+





+

+
+
+

+

+
+


+

+



+







+
+
+
+
+
9. The immediate precursor to compound S in this pathway is:
a) T; b) S; c) R; d) U; e) none of the above.
10. A mutation in gene 3 should lead to an accumulation in which metabolite in the pathway?
a) T; b) S; c) R; d) U; e) none of the above.