Number of Bacteria Resistant to T1 VirusAre Mutations Random orResistantResistantDirected by the Environment?coloniesCultureCulturecoloniesfoundOnce biologists appreciated that Mendelian traits were, infact, alternative versions of DNA sequences, whichresulted from mutations, a very important question aroseand needed to be answered: Are mutations random eventsnumberfoundnumber107111-10-120213that might happen anywhere on the DNA in a chromo-some, or are they directed to some degree by the environ-ment? For example, do the mutagens in cigarettes damageDNA at random locations, or do they preferentially seekout and alter specific sites such as those regulating thecell cycle?This key question was addressed and answered in anelegant, deceptively simple experiment carried out in 1943by two of the pioneers of molecular genetics, SalvadoreLuria and Max Delbruck. They chose to examine a particu-lar mutation that occurs in laboratory strains of the bacte-rium E. coli. These bacterial cells are susceptible to T1viruses, tiny chemical parasites that infect, multiply within,and kill the bacteria. If 105 bacterial cells are exposed to1010 T1 viruses, and the mixture is spread on a culture dish,not one cell grows-every single E. coli cell is infectedand killed. However, if you repeat the experiment using 10bacterial cells, lots of cells survive! When tested, thesesurviving cells prove to be mutants, resistant to T1 infec-tion. The question is, did the T1 virus cause the mutations,or were they present all along, too rare to be present in asample of only 105 cells but common enough to be presentin 109 cells?3014041150-5165-6170 -7641819035 -20103-5 -01- 2O- 13-15 2107-1 35-14-1Analysis1. Applying Concepts Is there a dependent variable inthis experiment? Explain.2. Interpreting DataT1-resistant colonies found in the 20 individualWhat is the mean number ofcultures?3. Making InferencesComparing the 20 individual cultures, do thecultures exhibit similar numbers of T1-resistantа.bacterial cells?b. Which of the two alternative outcomes illustrated,(a) or (b), is more similar to the outcome obtainedby Luria and Delbruck in this experiment?Drewing Conclusions Are these data consistentwith he hypothesis that the mutation for T1 resistanceamong E. coli bacteria is caused by exposure to TIvius? Explain.To answer this question, Luria and Delbruck devised asimple experiment they called a "fluctuation test," illustratedhere. Five cell generations are shown for each of foorindependent bacterial cultures, all tested for resistance in thfifth generation. If the T1 virus causes the mutations (toprow), then each culture willhave more or less the sameCufure 2Culture 1Culture 3Culture 4number of resistant cells, withonly a little fluctuation (that is,variation among the four). If, onthe other hand, mutations arespontaneousequally likely to occur in anygeneration,culturesand therefore0 0 0 0 0 0 Q 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 Q 00 0AA0000 00000thenbacterial00000006000600000 Ó66006000000 00000 000000000000000 000000inwhichT1-resistance mutation occurstheа.in earliergenerations willpossess far more resistant cellsby the fifth generation thancultures in which the mutationCulture 1Culture 2Culture 3Culture 4occurs in later generations,resulting in wide fluctuationamong the four cultures. Thetable presents the dataobtained for 200 0O 00 0 0 0 0 0OO 0 00 O 0 0 0 0 0 O0000000000000 6660000000000000 66000000000006600theyindividual0000000000000000 000cultures.b.Inquiry & AnalysisO O9

Question
Asked Sep 20, 2019

#1 

Number of Bacteria Resistant to T1 Virus
Are Mutations Random or
Resistant
Resistant
Directed by the Environment?
colonies
Culture
Culture
colonies
found
Once biologists appreciated that Mendelian traits were, in
fact, alternative versions of DNA sequences, which
resulted from mutations, a very important question arose
and needed to be answered: Are mutations random events
number
found
number
107
11
1-
1
0-
12
0
2
13
that might happen anywhere on the DNA in a chromo-
some, or are they directed to some degree by the environ-
ment? For example, do the mutagens in cigarettes damage
DNA at random locations, or do they preferentially seek
out and alter specific sites such as those regulating the
cell cycle?
This key question was addressed and answered in an
elegant, deceptively simple experiment carried out in 1943
by two of the pioneers of molecular genetics, Salvadore
Luria and Max Delbruck. They chose to examine a particu-
lar mutation that occurs in laboratory strains of the bacte-
rium E. coli. These bacterial cells are susceptible to T1
viruses, tiny chemical parasites that infect, multiply within,
and kill the bacteria. If 105 bacterial cells are exposed to
1010 T1 viruses, and the mixture is spread on a culture dish,
not one cell grows-every single E. coli cell is infected
and killed. However, if you repeat the experiment using 10
bacterial cells, lots of cells survive! When tested, these
surviving cells prove to be mutants, resistant to T1 infec-
tion. The question is, did the T1 virus cause the mutations,
or were they present all along, too rare to be present in a
sample of only 105 cells but common enough to be present
in 109 cells?
3
0
14
0
4
1
15
0-
5
16
5-
6
17
0 -
7
64
18
19
0
35 -
20
10
3-
5 -0
1- 2
O- 1
3-1
5 2
107-1 35-1
4-1
Analysis
1. Applying Concepts Is there a dependent variable in
this experiment? Explain.
2. Interpreting Data
T1-resistant colonies found in the 20 individual
What is the mean number of
cultures?
3. Making Inferences
Comparing the 20 individual cultures, do the
cultures exhibit similar numbers of T1-resistant
а.
bacterial cells?
b. Which of the two alternative outcomes illustrated,
(a) or (b), is more similar to the outcome obtained
by Luria and Delbruck in this experiment?
Drewing Conclusions Are these data consistent
with he hypothesis that the mutation for T1 resistance
among E. coli bacteria is caused by exposure to TI
vius? Explain.
To answer this question, Luria and Delbruck devised a
simple experiment they called a "fluctuation test," illustrated
here. Five cell generations are shown for each of foor
independent bacterial cultures, all tested for resistance in th
fifth generation. If the T1 virus causes the mutations (top
row), then each culture will
have more or less the same
Cufure 2
Culture 1
Culture 3
Culture 4
number of resistant cells, with
only a little fluctuation (that is,
variation among the four). If, on
the other hand, mutations are
spontaneous
equally likely to occur in any
generation,
cultures
and therefore
0 0 0 0 0 0 Q 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 Q 0
0 0
AA
0000 00000
then
bacterial
00000006000600000 Ó66006000000 00000 00000000000
0000 000000
in
which
T1-resistance mutation occurs
the
а.
in earlier
generations will
possess far more resistant cells
by the fifth generation than
cultures in which the mutation
Culture 1
Culture 2
Culture 3
Culture 4
occurs in later generations,
resulting in wide fluctuation
among the four cultures. The
table presents the data
obtained for 20
0 0
O 0
0 0 0 0 0 0
OO 0 0
0 O 0 0 0 0 0 O
0000000000000 6660000000000000 66000000000006600
they
individual
000000000
0000000 000
cultures.
b.
Inquiry & Analysis
O O9
help_outline

Image Transcriptionclose

Number of Bacteria Resistant to T1 Virus Are Mutations Random or Resistant Resistant Directed by the Environment? colonies Culture Culture colonies found Once biologists appreciated that Mendelian traits were, in fact, alternative versions of DNA sequences, which resulted from mutations, a very important question arose and needed to be answered: Are mutations random events number found number 107 11 1- 1 0- 12 0 2 13 that might happen anywhere on the DNA in a chromo- some, or are they directed to some degree by the environ- ment? For example, do the mutagens in cigarettes damage DNA at random locations, or do they preferentially seek out and alter specific sites such as those regulating the cell cycle? This key question was addressed and answered in an elegant, deceptively simple experiment carried out in 1943 by two of the pioneers of molecular genetics, Salvadore Luria and Max Delbruck. They chose to examine a particu- lar mutation that occurs in laboratory strains of the bacte- rium E. coli. These bacterial cells are susceptible to T1 viruses, tiny chemical parasites that infect, multiply within, and kill the bacteria. If 105 bacterial cells are exposed to 1010 T1 viruses, and the mixture is spread on a culture dish, not one cell grows-every single E. coli cell is infected and killed. However, if you repeat the experiment using 10 bacterial cells, lots of cells survive! When tested, these surviving cells prove to be mutants, resistant to T1 infec- tion. The question is, did the T1 virus cause the mutations, or were they present all along, too rare to be present in a sample of only 105 cells but common enough to be present in 109 cells? 3 0 14 0 4 1 15 0- 5 16 5- 6 17 0 - 7 64 18 19 0 35 - 20 10 3- 5 -0 1- 2 O- 1 3-1 5 2 107-1 35-1 4-1 Analysis 1. Applying Concepts Is there a dependent variable in this experiment? Explain. 2. Interpreting Data T1-resistant colonies found in the 20 individual What is the mean number of cultures? 3. Making Inferences Comparing the 20 individual cultures, do the cultures exhibit similar numbers of T1-resistant а. bacterial cells? b. Which of the two alternative outcomes illustrated, (a) or (b), is more similar to the outcome obtained by Luria and Delbruck in this experiment? Drewing Conclusions Are these data consistent with he hypothesis that the mutation for T1 resistance among E. coli bacteria is caused by exposure to TI vius? Explain. To answer this question, Luria and Delbruck devised a simple experiment they called a "fluctuation test," illustrated here. Five cell generations are shown for each of foor independent bacterial cultures, all tested for resistance in th fifth generation. If the T1 virus causes the mutations (top row), then each culture will have more or less the same Cufure 2 Culture 1 Culture 3 Culture 4 number of resistant cells, with only a little fluctuation (that is, variation among the four). If, on the other hand, mutations are spontaneous equally likely to occur in any generation, cultures and therefore 0 0 0 0 0 0 Q 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Q 0 0 0 AA 0000 00000 then bacterial 00000006000600000 Ó66006000000 00000 00000000000 0000 000000 in which T1-resistance mutation occurs the а. in earlier generations will possess far more resistant cells by the fifth generation than cultures in which the mutation Culture 1 Culture 2 Culture 3 Culture 4 occurs in later generations, resulting in wide fluctuation among the four cultures. The table presents the data obtained for 20 0 0 O 0 0 0 0 0 0 0 OO 0 0 0 O 0 0 0 0 0 O 0000000000000 6660000000000000 66000000000006600 they individual 000000000 0000000 000 cultures. b. Inquiry & Analysis O O9

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check_circleExpert Solution
Step 1

Any type of factor, condition, or trait that can be present in a different amount in the experiment is termed as a variable. An experiment contains three types of variables, dependent variable, independent variable, and controlled variable. The value or amount of the independent variable is changed by the scientist. While the value of dependent variable is based on the value of independent variable. The value of controlled variable remains constant during the whole experiment.

Step 2

The number of resistant colonies is the dependent variable in the given experiment. This is because in the number of resistant colonies in the culture is dependent on the amount of T1 virus present in the same culture. If the amount of T1 virus is almost equal to the numbe...

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