6.3: Manipulating genomes

Question 1

Name the enzyme that can be used to convert mRNA to single-stranded DNA. f215 june 14 q2di

Answer 1

reverse transcriptase

Question 2

In a colony of bees, about 5% of the workers are more adventurous than other workers. These bees are known as scout bees. They actively seek out new food sources and, if necessary, new nest sites.
Researchers investigated how gene expression differed in the brains of the scout bees
compared to the normal worker bees.
• The researchers extracted mRNA from the brain cells of normal worker bees.
• This mRNA was used to produce lengths of single-stranded DNA, which were then attached to a fluorescent dye.
• These lengths of single-stranded DNA were used as gene probes fixed onto a device known as a ‘microarray DNA chip’.
• mRNA extracted from the brain cells of
scout bees would only bind to the gene probes that matched it, causing these probes to fluoresce.
• The locations of the brightest fluorescent spots on the DNA chip revealed which genes were most active.
Explain how the locations of the fluorescent spots on the DNA chip reveal which genes
are most active. (3mks) f215 june 14 q2dii

Answer 2

1 mRNA binds to, (gene) probes/ cDNA/ ssDNA, by complementary base pairing;
2 the MORE active the gene the MORE mRNA produced;
3 during transcription;
4 MORE fluorescence indicates MORE mRNA (bound);

Question 3

The researchers found many differences in gene activity in scout bees compared to the normal worker bees. One of these differences in an activity was the gene used to make the neurotransmitter, dopamine.
In a follow up experiment, scout bees became less adventurous if dopamine signalling was prevented.
Use your knowledge of DRD4 receptors in humans to comment on the findings of this research in scout bee behaviour. f215 june14 2diii

Answer 3

1 dopamine linked to, ADHD / addiction / risk-taking / 1 adventurous behaviour / hyperactivity / erratic behaviour (in humans);
2 common mechanism in bees and humans (for adventurous behaviour); [e.g. BOTH have, DRD4 /dopamine receptors; e.g. dopamine has the same effect in BOTH]
3 as they are different organisms the mechanisms may not be comparable (even though apparently similar);
4 e.g. other genes also involved in, bee / human, behaviour
[Note: ‘both have dopamine receptors which are linked to adventurous behaviour’ = 1 mk; ‘both have dopamine receptors and dopamine is linked to adventurous behaviour’ = 2 mks]

Question 4

Outline the roles of each of the following procedures in sequencing a genome:
(i) the polymerase chain reaction (PCR)

Answer 4

to, amplify / make (many) copies of, DNA ;
(range of) different lengths; [idea of, chain terminating / dideoxy, nucleotides attaching at different points along sequence]

Question 5

Outline the roles of each of the following procedures in sequencing a genome:
(ii) electrophoresis

Answer 5

to put DNA pieces in size order ;

to read, base sequence / order of bases;

Question 6

Outline the roles of each of the following procedures in sequencing a genome:
(iii) digestion of DNA by restriction enzymes.

Answer 6

to cut (genome DNA) into, small(er) / 750 bp, fragments ; [fragment size in range 500-1000 base pairs]
to cut, vectors / BACs / plasmids, (for gene library) ;

Question 7

Suggest why a genome has to be fragmented before sequencing.

Answer 7

genome, too big / very large ; [only, small sections / 750bp, can be sequenced (at a time)]
accuracy better / fewer errors (with small fragments) ;[large sections sequenced less accurately]
divide job over, time / different labs ; [otherwise would take TOO long / be unmanageable / be impractical]

Question 8

Monkey flower and blueberry belong to the same taxonomic group within the plant kingdom. Only one of the pair was chosen for further sequencing work.
Using the data in Table 5.1, suggest reasons why monkey flower was chosen instead of blueberry. (2mks) [f215 june 13 q5]

Answer 8

(monkey flower) has, smaller genome / fewer Mbp DNA ;

fewer lab hours / fewer staff needed / quicker / cheaper;

Question 9

Use your knowledge of the effects of polyploidy in bread wheat to suggest one way in which the fruit of a hexaploid (6n) blueberry might differ in appearance from that of a diploid (2n) blueberry.

Answer 9

larger (in size); [bigger/ plumper/ juicer]

Question 10

DNA sequence information is most useful when used with the phylogenetic (cladistic) approach to classification. How does the phylogenetic approach to classifying species differ from the biological species
concept? (2mks)

Answer 10

phylogenetic approach no need to test for interbreeding ; [for biological species concept – (importance of members of same species) (inter)breeding to give fertile offspring]
ref. common ancestor / monophyletic groups ;
can apply to organisms that reproduce asexually ; [biological species concept – doesn’t apply to asexually reproducing organisms]
can apply to, extinct organisms / fossils ; [biological species concept – doesn’t apply to, extinct organisms / fossils]