Download The diagram below shows a partial sequence of nucleotide bases

PROCTOR VERSION
3.24 C: Change in Phenotype Quiz
1.
The diagram below shows a partial sequence of nucleotide bases for the normal hexosaminidase
A (HEXA) protein and the resulting amino acid sequence.
Tay-Sachs disease is caused by a lack of normal HEXA proteins, which leads to a buildup of cell
membrane compounds in nerve cells, eventually leading to impaired mental and physical
abilities. The four-base insertion that causes Tay-Sachs disease in the allele that codes for the
HEXA protein is shown below.
The chart below shows the amino acids produced by each possible combination of three RNA
bases.
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PROCTOR VERSION
3.24 C: Change in Phenotype Quiz
Which statements best explain how this insertion will affect the HEXA protein?
(A) The insertion will not change the first two amino acids, but the Ser and Tyr amino acids will
be changed to new amino acids. The amino acids that follow Tyr will remain the same,
because they are not affected by the insertion.
Distractor Rationale:
This answer suggests the student may understand that inserting extra nucleotides into a
gene will disrupt the amino acid sequence where the insertion occurs, but does not
understand that the amino acids “downstream” from the insertion will also be altered
because the insertion of four nucleotides frameshifts the codons (shifts the bases in each of
the subsequent codons).
(B) The insertion will not change the first three amino acids, but the next four amino acids will be
altered. Protein synthesis will stop after the seventh amino acid, because the insertion has
changed the coding instructions on the mRNA.
Rationale:
This answer suggests the student understands that if the four bases are inserted into the
gene, the first codon affected (UCC) will remain the same because UCC and UCU both
code for the Ser amino acid; however, the next four amino acids will be changed due to the
frameshift of the mRNA strand, and the eighth codon will now be a stop codon.
(C) The insertion will affect all but the first amino acid, so all of the amino acids after Ile will be
different. The protein will be abnormally large, because the stop codon will be changed to
code for an amino acid.
Distractor Rationale:
This answer suggests the student may understand that the first codon affected (UCC) will
remain the same because UCC and UCU both code for the Ser amino acid, and that the
codons that follow will all be changed due to the frameshift, but does not understand that
the polypeptide will stop prematurely because the eighth codon will be changed to a stop
codon.
(D) The insertion will not change any of the existing amino acids in the sequence. An additional
amino acid (Ile) will be inserted, because the additional codon will result in an extra amino
acid in the sequence.
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PROCTOR VERSION
3.24 C: Change in Phenotype Quiz
Distractor Rationale:
This answer suggests the student may understand that inserting four bases into the gene
will result in the insertion of the Ile amino acid into the protein, but does not understand
that the amino acids “downstream” from the insertion will also be changed because the
insertion of four nucleotides frameshifts the codons (shifts the bases in the mRNA strand).
Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype
2.
Environmental agents such as nuclear radiation can damage DNA by breaking the bonds
between oxygen (O) and phosphorus (P) in the “backbone” of DNA, as shown in the diagram
below.
Cells with broken DNA will attempt to repair the broken ends by joining the free ends to other
pieces of DNA within the cell. This repair can create a type of mutation called translocation when
DNA is placed in the wrong location.
Which statement provides the most likely explanation for the mutation that would result in a
cancerous cell?
(A) Nuclear radiation causes a translocation in a gene that is required to synthesize the spindle
during cell division.
Distractor Rationale:
This answer suggests the student may understand that a translocation in a gene that allows
for spindle formation would affect the process of cell division, but does not understand that
this would prevent cells from dividing, because the spindle is required for cell division, and
cancer involves rapid cell division in body cells.
(B) Nuclear radiation causes a translocation of a gene segment that produces a protein involved
in the unraveling of chromosomes to form chromatin.
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PROCTOR VERSION
3.24 C: Change in Phenotype Quiz
Distractor Rationale:
This answer suggests the student may understand that a translocation of a segment of a
gene involved in the unraveling of chromosomes would affect the process of cell division in
affected cells, but does not understand that this would most likely lead to cell death, not
cancer, because it would prevent cells from entering the growth phase (interphase).
(C) Nuclear radiation causes a translocation in a gene that produces a ribosomal protein
involved in protein synthesis.
Distractor Rationale:
This answer suggests the student may understand that a translocation in a gene involved in
translation may affect protein synthesis, but does not understand that this would probably
not result in cancer because such a mutation is more likely to result in cell death.
(D) Nuclear radiation causes the translocation of a segment of a regulatory gene that normally
keeps cells from entering the mitotic stage of the cell cycle.
Rationale:
This answer suggests the student understands that a translocation removing part of a gene
that suppresses cell division could lead to cancer because cancer begins in cells in which
the process of cell division is not properly regulated.
Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype
3.
The four major blood groups in humans are determined by the presence or absence of two
proteins, antigen A and antigen B, on the surface of red blood cells, as shown in the table below.
The mutation shown in the diagram below occurs on the gene that codes for the A antigen in
bone marrow cells that normally produce type A red blood cells. The nucleotide sequences that
code for the A and B antigens differ from each other by seven nucleotide substitutions, which
translate into four amino acids that differ between the antigen products.
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PROCTOR VERSION
3.24 C: Change in Phenotype Quiz
Which statement best explains how this deletion affects the phenotype of the cells with the
mutation?
(A) Affected cells will still be type A because only one base will be deleted, and therefore, there
will most likely be only a slight change in the A antigen.
Distractor Rationale:
This answer suggests the student may understand that a nucleotide deletion will disrupt the
amino acid where the deletion occurs, but does not understand that all the triplets that
code for the amino acids after that point will also be changed because each additional codon
is shifted, which usually results in significant changes in the amino acid sequence and the
resulting protein structure. Without the A antigen, the red blood cells will result in type O
blood.
(B) Affected cells will become type O instead of type A because the deletion will render the A
allele non-functional, and this lack of antigens will yield the type O phenotype.
Rationale:
This answer suggests the student understands that if a single base deletion occurs in the
gene, all of the triplets that code for the amino acids after that point will be changed because
each additional codon will be shifted, and this will result in significant changes in the amino
acid sequence and resulting protein structure, and will most likely render the protein nonfunctional. Without the production of A antigens, red blood cells that would normally be type
A will now be type O (neither A nor B antigens on the red blood cells).
(C) Affected cells will become type B instead of type A because the deletion will change the A
allele so that it produces a new antigen, which will be the type B phenotype.
Distractor Rationale:
This answer suggests the student may understand that a nucleotide deletion will disrupt the
polypeptide and create a different protein, but does not understand that the cells will not be
type B because there is very little chance that this new polypeptide sequence will produce
the exact sequence of nucleotides necessary to produce the B antigen.
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PROCTOR VERSION
3.24 C: Change in Phenotype Quiz
(D) Affected cells will become type AB instead of type A because the deletion will change part of
the genetic message for the A allele so that it produces both A and B antigens.
Distractor Rationale:
This answer suggests the student may understand that a nucleotide deletion will disrupt part
of the polypeptide after the deletion and that the genetic sequence before the deletion will be
the same, but does not understand that this will not produce the AB phenotype because
this phenotype would require a fully functional A antigen and a fully functional B antigen, and
the A antigen will not be present after the deletion.
Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype
4.
Polypeptides are comprised of amino acids, which differ in chemical structure, and, in turn, have
different physical and chemical properties. The diagram below shows a partial normal gene and
polypeptide, as well as a mutation due to a change in one base, and the resulting polypeptide.
Which statement best explains the expected change in the polypeptide produced from the DNA
with the mutation, compared to the normal polypeptide?
(A) The mutation will likely result in a large, nonfunctional polypeptide, because the insertion of
the T base will change all of the DNA triplets that are read “downstream,” including the stop
codon, and a large, deformed polypeptide with different physical and chemical properties will
result.
Distractor Rationale:
This answer suggests the student may understand that an insertion mutation shifts all DNA
triplets after the mutation and often causes major changes in polypeptides. However, the
student does not understand that a frameshift will not occur as a result of this mutation,
because one base is substituting for another, so there will be no change to other amino
acids in the polypeptide.
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PROCTOR VERSION
3.24 C: Change in Phenotype Quiz
(B) The mutation will not change the polypeptide, because only one base out of several hundred
bases has been changed, and this single base change will not result in any significant
difference in the physical, chemical, or functional properties of the polypeptide.
Distractor Rationale:
This answer suggests the student may understand that a one-base substitution often causes
little or no change in a polypeptide, but does not understand that there is no evidence
supporting this claim for this mutation because the base change codes for a different amino
acid, and one cannot assume that the two amino acids have the same chemical and
physical properties.
(C) The mutation will likely result in a polypeptide with a different shape or structure, because
valine may have different chemical and physical properties than glutamic acid, and this may
cause the polypeptide to fold into a different shape.
Rationale:
This answer suggests the student understands that if this mutation results in a different
amino acid in the polypeptide, changes in protein structure and function may result,
depending on how the new amino acid interacts with other amino acids and/or the external
environment.
(D) The mutation will result in little or no change in the polypeptide, because valine is already
present in the amino acid chain, so the mutation will not significantly change the physical or
chemical properties of the polypeptide.
Distractor Rationale:
This answer suggests the student may understand that valine is already coded for in the
polypeptide, but does not understand that valine replacing a glutamic acid could produce a
change in the polypeptide if the two amino acids have significantly different chemical or
physical properties.
Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype
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