Download University of York Department of Biology B. Sc Stage 1 Degree

BIO00007C
Examination Candidate Number: _____________
Desk Number: _____________
University of York
Department of Biology
B. Sc Stage 1 Degree Examinations 2016-17
Genetics
Time allowed: 1 hour and 30 minutes
Total marks available for this paper: 50
● Answer ​all​ questions in the spaces provided on the examination paper
● The marks available for each question are indicated on the paper
● A calculator will be provided
For marker use only:
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BIO00007C
Answer all questions in the spaces provided
1. In a cell with a diploid number of chromosomes of 8 undergoing meiosis,
one chromosome failed to replicate its centromere and disjunction did
not take place.
a) ​ A
​ t what phase of meiosis did this happen?
​(1 mark)
b)​ ​State the number of chromosomes in each of the four gametes
generated from this cell.
​(1 mark)
the space above this line should be sufficient for your answer
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BIO00007C
2. In a certain breed of cats, eyes can be blue (B) or grey (b), the tail can
be rigid (R) or stumpy (r) and hair can be long (Q) or short (q). B, R and
Q are the dominant alleles and the three genes are on different
chromosomes.
a) “Bella” is a cat that shows the three dominant traits. Indicate the
genotype of the cat you should cross Bella with in order to determine
Bella’s genotype.
​(1 mark)
b) All of the progeny of the cross described in (a) have blue eyes and
long hair, however half have a stumpy tail and half have a rigid tail. What
is Bella’s genotype?
​(1 mark)
c) What fraction of the offspring from the cross BBRrQq X BbrrQq would
be blue-eyed with stumpy tail and short hair?
​(2 marks)
d) The cross above produced 64 cats from several matings. How many
cats would be predicted to have the genotype BBrrqq?
​(2 marks)
Turn over
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BIO00007C
3. You are repeating a genetic cross in flies to confirm the genetic map
below:
Fv-----0.6cM---------Sh------22cM-------Df
a)​ ​From the cross between a triple heterozygote (Fv Sh Df/+ + +) with a
triple homozygous recessive (Fv Sh Df/ Fv Sh Df), complete the table
of anticipated phenotypic numbers you would expect in 1000 progeny
assuming that only parental and single crossover classes are
produced.
​(3 marks)
Fv Sh Df
+ + +
Fv +
+
+ Sh Df
+ + Df
Fv Sh +
b)​ W
​
hat would be the probability of a double crossover?
​(1 mark)
c)​ ​How many double crossover progeny individuals are expected in 1000
flies?
​(1 mark)
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BIO00007C
4. The pedigree illustrated here shows individual II-2 affected with a
disease that is inherited in an autosomal recessive pattern. “A”
represents the dominant allele and “a”​ represents the recessive allele.
a) What is the genotype of I.1?
​(1 mark)
b)​ W
​
hat are the possible genotypes of II.1?
​(1 mark)
c)​ ​What is the probability that if parents I-1 and I-2 had another child, he or
she would not have the disease?
​(1 mark)
d)​ W
​
hat is the probability that II.1 is a disease carrier?
​(1 mark)
the space above this line should be sufficient for your answer
Turn over
page 5 of 11
BIO00007C
5. The following DNA sequence is from a wild-type protein-coding
prokaryotic gene and includes the start codon:
5’-AGATGGGTAACTGGGATTTT-3’
3’-TCTACCCATTGACCCTAAAA-5’
a) Which strand of the DNA is the template strand if the gene is
transcribed? Provide an explanation for your answer.
​(1 mark)
b) Which polypeptide will be produced from the start of the open-reading
frame? A genetic code table is provided at the end of the question.
(1 mark)
the space above this line should be sufficient for your answer
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BIO00007C
c) Three sequences, each containing either a single base-substitution,
single base-insertion or single base-deletion compared to the wild-type
sequence given above, are listed below. For each sequence state
whether the consequence will be a frame-shift mutation, a non-sense
mutation, a mis-sense mutation or a silent mutation.
​(3 marks)
i)
5’-AGATGGGAACTGGGATTTT-3’
3’-TCTACCCTTGACCCTAAAA-5’
ii)
5’-AGATGGGTAACTGAGATTTT-3’
3’-TCTACCCATTGACTCTAAAA-5’
iii)
5’-AGATGGGTAACTGGGATCTT-3’
3’-TCTACCCATTGACCCTAGAA-5’
Turn over
page 7 of 11
BIO00007C
6. The following table indicates whether the CAP activator protein and/or
the LacI repressor protein are binding to their sites within the regulatory
region of the ​lac operon of ​E. coli bacteria grown in four different growth
media.
a) Fill in the table indicating whether you expect Glucose and/or Lactose
to have been present in the different growth media.
​(4 marks)
Growth media
CAP activator
binding?
LAC repressor
binding?
1
No
No
2
No
Yes
3
Yes
Yes
4
Yes
No
Glucose?
Lactose?
b) Which growth condition will give rise to the highest level of expression
of the ​lac operon? Provide an explanation for your answer.
​(2 marks)
the space above this line should be sufficient for your answer
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BIO00007C
7. a) Rifampicin is an antibiotic that inhibits the bacterial RNA polymerase.
The figure below shows the mRNA transcript levels of two genes, ​mccA
and ​mccB, measured over time following the addition of rifampicin to a
bacterial cell culture. Provide an explanation for the results observed.
(2 marks)
b) Cycloheximide and edeine are both chemical inhibitors of translation.
When cells are treated with cycloheximide, translation is inhibited
immediately. When cells are treated with edeine, translation continues
for some minutes before stopping. Suggest at which stage of translation
cycloheximide and edeine are acting and provide an explanation for your
answer.
i) Cycloheximide
​(2 marks)
ii) Edeine
​(2 marks)
Turn over
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BIO00007C
8. You are provided with purified plasmid DNA (cloning vector) and purified
human genomic DNA containing the sequence of interest (see pictures
below).
a) Describe how you could insert the genomic sequence of interest into
the EcoRI restriction site of the cloning vector.
​(5 marks)
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BIO00007C
b) After transformation of ​E. coli with the resulting DNA and isolation of
plasmid DNA from several ​E. coli clones, you carry out a diagnostic
restriction digest. Digestion with which restriction enzyme would give you
information about whether the DNA of interest was successfully inserted
into the vector, and about the orientation of the insert?
​(1 mark)
c) List the DNA fragment sizes that you would obtain after digestion with
this restriction enzyme.
(3 marks)
i) Empty plasmid:
ii) Plasmid with insert (one orientation):
iii) Plasmid with insert (other orientation):
d) Explain the function of the lacZ gene in the cloning vector. ​(4 marks)
9. Explain why Lederberg and Tatum’s experiments with auxotrophic
bacterial strains suggested the exchange of genetic material between
bacteria.
​ (3 marks)
End of exam
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