Genetics Final Exam: Comprehensive Explanations,
Correct Solutions, and Diverse Questions with
Thorough Answer Analysis
We isolate nine different mutants unable to make histidine. They map in differentlocations,
by genetics means we can show there are nine different genes in the pathway.How many
enzymes can we anticipate finding in this pathway?A) 1
B) 3
C) 6
D) 9
E) 12 - CORRECT ANSWER- -D) 9
A bacterium is found that is resistant to the antibiotic gentimycin. The bacterium
wasisolated in a hospital where patients were routinely given gentimycin for a variety of
infections. What was the selective pressure driving development of this resistant
population?
A) Presence of gentimycin in the environment
B) High mutation rate for the bacterium.
C) Growth situation for the bacterium.
D) Patients not receiving antibiotic provided source of bacteria
E) None of the above - CORRECT ANSWER- -A) Presence of gentimycin in the environment
he bacterial chromosome is:
A) circular
B) covalently closed
C) 1 strand DNA
D) contains mobile sequences
,E) all of the above - CORRECT ANSWER- -E) all of the above
Another mutation for penicillin resistance is in an enzyme called a β-lactamase.Penicillin is
a β-lactam. Changes in the amino acid composition of the enzyme result init being able to
degrade penicillin so it can't inhibit cell wall synthesis. What willhappen to a cell with this
mutation if penicillin is present in the environment?
A) Nothing, it will not be selected and will remain a very minor component of themicroflora.
B) Mutant bacterium will come to dominant the population.
C) Mutant bacterium will not grow normally.
D) Mutant bacterium will not form a normal cell wall.
E) None of these will happen - CORRECT ANSWER- -B) Mutant bacterium will come to
dominant the population
Organisms that lack a nuclear membrane and have no membrane-enclosed organelles are
termed:
A) bacteria.
B) archaea.
C) prokaryotes.
D) eukaryotes.
E) none of the above - CORRECT ANSWER- -C) prokaryotes
Bacterial numbers in the large intestine can exceed 1012
/gm in feces. There are perhapsa half dozen species that predominate this flora and
hundreds that play a very small role.The bacteria grow and die, often lyse releasing DNA
into the environment. What protects viable bacteria from this DNA?
A) Largely impermeable cytoplasmic membrane.
B) Capsule composed of polysaccharide surrounding the cell.
C) Restriction endonucleases in the cells that degrade foreign DNA.
D) Nucleases excreted by bacteria to degrade DNA into sugar and the bases.
,E) None of the above - CORRECT ANSWER- -C) Restriction endonucleases in the cells that
degrade foreign DNA
We spread 10^9 bacteria on a plate with 25 µg streptomycin/ml media. We get four
colonies to grow. These colonies include bacteria that are:
A) wild type.
B) resistant to streptomycin.
C) resistant to all antibiotics.
D) able to grow in unusual circumstance.
E) none of the above - CORRECT ANSWER- -B) resistant to streptomycin
We grow up the streptomycin resistant (Str ^r ) cells to 10^9 and plate them on medium
with 25 µg/ml gentimycin. We get six colonies to grow. These cells should be:
A) Str^r
B) Gen^r
C) Str ^r Gen^r
D) wild type
E) none of the above - CORRECT ANSWER- -C) Str^r Gen^r
We plate bacteria out on a plate covered with a normally virulent bacteriophage.
Twocolonies form. These bacteria in the colonies are now:
A) phage resistant
.B) phage sensitive.
C) wild type.
D) all of the above
E) none of the above - CORRECT ANSWER- -A) Phage Resistant
, How many plantings would it take to make a bacterium resistant to
streptomycin,gentimycin and a bacteriophage?A) 1
B) 2
C) 3
D) 4
E) 5 - CORRECT ANSWER- -C) 3
If resistance to streptomycin occurs about one in 10^9 cells (one amino acid gets
changedin one ribosomal protein), resistance to gentimycin occurs about one in 10^9
cells, howoften could you get double mutants, one that was mutated in both functions?
A) 10^9
B)10^18 (10^9×10^9)
C) 1
D) cannot estimate
E) none of the above - CORRECT ANSWER- -B)10^18 (10^9×10^9)
The Ames test for carcinogens uses
his- mutants of S. typhimurium. Carcinogens are mutagens, and cause mutations. These
mutants can be reverted, made to be his+ with common mutagens. We spread 10^8
bacteria on a plate and then add the putative mutagen/carcinogen on a piece of filter paper
and count the colonies around the filter paper. Lots of colonies mean lots of mutations, an
effective mutagen. We test two chemicals, A and B. One µg/ml A causes 14 colonies to
appear, one µg B causes 96 colonies to form. Which is the most potent mutagen?
A) A
B) B
C) A or B
D) none of the above
E) both A and B - CORRECT ANSWER- -B)B
Correct Solutions, and Diverse Questions with
Thorough Answer Analysis
We isolate nine different mutants unable to make histidine. They map in differentlocations,
by genetics means we can show there are nine different genes in the pathway.How many
enzymes can we anticipate finding in this pathway?A) 1
B) 3
C) 6
D) 9
E) 12 - CORRECT ANSWER- -D) 9
A bacterium is found that is resistant to the antibiotic gentimycin. The bacterium
wasisolated in a hospital where patients were routinely given gentimycin for a variety of
infections. What was the selective pressure driving development of this resistant
population?
A) Presence of gentimycin in the environment
B) High mutation rate for the bacterium.
C) Growth situation for the bacterium.
D) Patients not receiving antibiotic provided source of bacteria
E) None of the above - CORRECT ANSWER- -A) Presence of gentimycin in the environment
he bacterial chromosome is:
A) circular
B) covalently closed
C) 1 strand DNA
D) contains mobile sequences
,E) all of the above - CORRECT ANSWER- -E) all of the above
Another mutation for penicillin resistance is in an enzyme called a β-lactamase.Penicillin is
a β-lactam. Changes in the amino acid composition of the enzyme result init being able to
degrade penicillin so it can't inhibit cell wall synthesis. What willhappen to a cell with this
mutation if penicillin is present in the environment?
A) Nothing, it will not be selected and will remain a very minor component of themicroflora.
B) Mutant bacterium will come to dominant the population.
C) Mutant bacterium will not grow normally.
D) Mutant bacterium will not form a normal cell wall.
E) None of these will happen - CORRECT ANSWER- -B) Mutant bacterium will come to
dominant the population
Organisms that lack a nuclear membrane and have no membrane-enclosed organelles are
termed:
A) bacteria.
B) archaea.
C) prokaryotes.
D) eukaryotes.
E) none of the above - CORRECT ANSWER- -C) prokaryotes
Bacterial numbers in the large intestine can exceed 1012
/gm in feces. There are perhapsa half dozen species that predominate this flora and
hundreds that play a very small role.The bacteria grow and die, often lyse releasing DNA
into the environment. What protects viable bacteria from this DNA?
A) Largely impermeable cytoplasmic membrane.
B) Capsule composed of polysaccharide surrounding the cell.
C) Restriction endonucleases in the cells that degrade foreign DNA.
D) Nucleases excreted by bacteria to degrade DNA into sugar and the bases.
,E) None of the above - CORRECT ANSWER- -C) Restriction endonucleases in the cells that
degrade foreign DNA
We spread 10^9 bacteria on a plate with 25 µg streptomycin/ml media. We get four
colonies to grow. These colonies include bacteria that are:
A) wild type.
B) resistant to streptomycin.
C) resistant to all antibiotics.
D) able to grow in unusual circumstance.
E) none of the above - CORRECT ANSWER- -B) resistant to streptomycin
We grow up the streptomycin resistant (Str ^r ) cells to 10^9 and plate them on medium
with 25 µg/ml gentimycin. We get six colonies to grow. These cells should be:
A) Str^r
B) Gen^r
C) Str ^r Gen^r
D) wild type
E) none of the above - CORRECT ANSWER- -C) Str^r Gen^r
We plate bacteria out on a plate covered with a normally virulent bacteriophage.
Twocolonies form. These bacteria in the colonies are now:
A) phage resistant
.B) phage sensitive.
C) wild type.
D) all of the above
E) none of the above - CORRECT ANSWER- -A) Phage Resistant
, How many plantings would it take to make a bacterium resistant to
streptomycin,gentimycin and a bacteriophage?A) 1
B) 2
C) 3
D) 4
E) 5 - CORRECT ANSWER- -C) 3
If resistance to streptomycin occurs about one in 10^9 cells (one amino acid gets
changedin one ribosomal protein), resistance to gentimycin occurs about one in 10^9
cells, howoften could you get double mutants, one that was mutated in both functions?
A) 10^9
B)10^18 (10^9×10^9)
C) 1
D) cannot estimate
E) none of the above - CORRECT ANSWER- -B)10^18 (10^9×10^9)
The Ames test for carcinogens uses
his- mutants of S. typhimurium. Carcinogens are mutagens, and cause mutations. These
mutants can be reverted, made to be his+ with common mutagens. We spread 10^8
bacteria on a plate and then add the putative mutagen/carcinogen on a piece of filter paper
and count the colonies around the filter paper. Lots of colonies mean lots of mutations, an
effective mutagen. We test two chemicals, A and B. One µg/ml A causes 14 colonies to
appear, one µg B causes 96 colonies to form. Which is the most potent mutagen?
A) A
B) B
C) A or B
D) none of the above
E) both A and B - CORRECT ANSWER- -B)B
