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NCEA Level 3 Biology (90715) 2012 — page 1 of 3
Assessment Schedule – 2012
Biology: Describe the role of DNA in relation to gene expression (90715)
Assessment Criteria
Q
ONE
Achievement
Merit
Excellence
Describes transcription.
• Transcription is where the
DNA is opened and free
nucleotides attach making
to the mRNA strand via
base pairing.
Describes translation.
• Attaching to a ribosome,
where the codons are
matched to tRNAs carrying
amino acids in translation.
• The amino acids are joined
via peptide bonds to
produce a peptide chain.
Describes one way that the
faulty myostatin gene may
cause a change in
phenotype.
• The faulty gene produces
the wrong code for
transcription, so the mRNA
is wrong.
• The mutated gene cannot
produce the right protein.
• Frameshift in mRNA from
transcription will not be
translated translated
correctly.
Explains how transcription is
affected by deletion in the
myostatin gene.
• The loss of 11 base pairs / deletion
mutation means the DNA base
sequence / triplets is changed /
causes a reading frameshift, so that
the nucleotides that make the RNA
(codon) are now in a different
sequence / codons the RNA
sequence may now contain a
premature stop codon.
Explains how translation is
affected by deletion in the
myostatin gene.
• The RNA sequence (codon) is
changed / mutated sequence /
incorrect order which affects
formation of the amino acid chain /
polypeptide chain at the ribosome.
• Different tRNAs match from the
deletion point, bringing a different
arrangement of amino acids. A
stop codon may have been
produced prematurely, which stops
translation and results in a
shortened polypeptide chain.
Explains how the faulty gene can
cause changes to the expression of
phenotype.
• Change in the DNA code has an
effect on the order of amino acids /
polypeptide chain, which will
change the shape / structure /
phenotype / activity of the
myostatin protein.
• Change in DNA / mRNA code has
an effect on the final protein shape
which will effect phenotype /
activity of myostatin protein.
Discusses how a deletion mutation in
myostatin can affect gene expression
AND links a change in phenotype in
Belgian Blue cattle to its significance
for breeders.
• As the DNA sequence has 11 base
pairs deleted / mutated this will
change the order of base pairing
(concept of codons shifted because
of deletion / mutation) as the RNA is
synthesised during transcription.
This will affect the final mRNA
product, changing the codon
sequence (shortening the RNA
possibly disrupting a section of
coding RNA / exon). During
translation, the amino acid sequence
of the polypeptide will change (in
this case shortened to 288 amino
acids instead of 376). This can mean
that the final protein will not fold
properly / will be the wrong shape /
wrong structure and the active sites /
ability to connect with other proteins
will be blocked, so that the protein
cannot act to regulate muscle
development.
A = 2 × a statements
M = 2 × m statements
E=1×e
Farmers could breed cattle with the
faulty myostatin gene to produce
cattle with greater meat production
than other breeds and greater value
per head of cattle. (May also
mention that the double muscled
cattle could have health and
reproductive issues).
NCEA Level 3 Biology (90715) 2012 — page 2 of 3
TWO
Role of the repressor
molecule is described.
Eg, the repressor molecule
binds to the operator and
stops transcription / prevents
RNA polymerase binding
Control function of the
operon is described.
Eg, the operon acts as a
switch to allow transcription
of mRNA / production of
proteins / enzymes.
Describes the overall role /
importance of the operon.
Eg, the operon allows
bacteria to break down
lactose when it is present.
Eg, important for
conservation of energy for
bacterium.
Explains the roles of the inducer
and the repressor in the function of
the operon.
The repressor binds to the operator so
RNA polymerase cannot bind and
transcription is blocked. When an
inducer is present (lactose) it binds to
the repressor and inactivates it /
causes it to move off the operator site.
The operator region is open, RNA
polymerase can now bind to the
promotor and transcription happens.
Lactose digesting enzymes / proteins
can be made.
A = 2 × a statements
M = 2 × m statements
Explains that the action of the
operon means the bacteria do not
have to produce enzyme all the
time.
Eg, the bacteria will only produce
enzymes / proteins when lactose is
present, instead of producing it all the
time therefore saving energy for the
bacterium.
Provides an in-depth explanation of
the role of the repressor and
inducer in lactose digestion.
The repressor binds to the operator so
RNA polymerase cannot bind and
transcription is blocked. When an
inducer is present (lactose) it binds to
the repressor and inactivates it /
causes it to move off the operator site.
The operator region is open, RNA
polymerase can now bind to the
promotor and transcription happens.
Lactose digesting enzymes can be
made.
As the lactose is removed / broken
down the inducer disappears and the
repressor is again activated, so it
binds again to the operator, blocking
further transcription.
AND
Discusses the importance of the
operon mechanism to the E. coli
bacterium.
Eg, lactose acts as the inducer to
prevent the repressor binding. The
importance of this is that the
mechanism for enzyme production is
only switched on in the presence of
lactose, which ensures the food
supply is digested but avoids
unnecessary enzyme production when
the substrate is absent / operon is
efficient and saves energy.
E=1×e
NCEA Level 3 Biology (90715) 2012 — page 3 of 3
THREE
• Describes the genotypes
as PPcc for the white seed
and ppCC for the red
seed.
AND
Completes a Punnett
square with no errors
that shows why all
offspring must be PpCc
genotype.
OR
Describes the genotypes
as PPcc for the white seed
and ppCC for the red
seed.
AND
Correct description of
why offspring has PpCc
genotype.
Eg, offspring will be PpCc
because one parent has
given them Pc and the
other parent has given
them pC.
• Describes a metabolic
pathway.
Eg, series of chemical
reactions OR through an
annotated diagram.
Produces evidence for the outcome
and explains the outcome as a gene
interaction and result from a
metabolic pathway.
Purple C-PWhite ccPRed C-pp
Only C allele will allow colour
expression.
Then only P allele will convert /
make to purple / pigment. In this case
for all purple seeds to be produced by
a white-seeded and red-seeded plant,
there must have been two dominant
alleles present for each of C and P
genes.
This is an example of a gene
interaction (epistasis / supplementary)
where the expression of one gene will
effect the expression of another gene
Metabolic pathway is defined or
represented by a diagram
Eg, series of chemical reactions
where one product / substrate is the
starting molecule (precursor) for the
next reaction (intermediate / final
product).
• Describes the outcome as
an interaction between
two genes (epistasis /
supplementary).
A=2×a
M=1×m
Uses Punnett square / explanation
to derive a diagram used to discuss
the outcome from the gene
interactions (in terms of dominant
and recessive alleles and their
action on converting precursor
molecules into intermediate and
final products).
Eg
(Gene C )
Enzyme C
White (__cc) → expression
Precursor
Intermediate
(Gene P)
Enzyme P
purple / red (P_ C_) / red (pp C _)
final product
Dominant C allele required to convert
colourless precursor into pigmented
intermediate. Dominant P allele
required to convert pigment into
purple. If P allele is not present /
mutant / recessive, red only will be
expressed. If c / recessive allele is
present / C allele is absent, no colour
will be expressed at all, regardless of
presence of P allele. This is an
interaction between genes (called
epistasis / supplementary interaction)
where the expression of one gene will
effect the expression of another gene.
AND
Metabolic pathway is defined or
represented by a diagram
Eg, series of chemical reactions that
are controlled by enzymes where one
product / substrate is the starting
molecule (precursor) for the next
reaction (intermediate / final product).
E=1×e
Judgement Statement – 2012
Achievement
Achievement with Merit
Achievement with Excellence
2A
2M
2E