Download The diagram below shows a partial sequence of nucleotide bases

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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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.
(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.
(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.
(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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3.24 C: Change in Phenotype Quiz
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.
(B) Nuclear radiation causes a translocation of a gene segment that produces a protein
involved in the unraveling of chromosomes to form chromatin.
(C) Nuclear radiation causes a translocation in a gene that produces a ribosomal protein
involved in protein synthesis.
(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.
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3.24 C: Change in Phenotype Quiz
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.
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.
(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.
(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.
(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.
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3.24 C: Change in Phenotype Quiz
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.
(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.
(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.
(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.
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