Lac Operon Genetics
Practical 2. Analysis of wild type and lac operon mutant strains of the bacterium Escherichia coli
Complete the results tables below using the data you obtained in the practical.
Describe the size, colour and eosin sheen of the colonies on the EMB plates in Table 1 below.
Strain
Size
Colour
Eosin sheen
WT
Large colonies purple
Strong eosin sheen
H
Large colonies purple
Weak eosin sheen
J
Small colonies pink
No eosin sheen
K
Small colonies pink
No eosin sheen
Fill in the fluorescence results for NA+glu and NA+lac in Table 2 below.
Strain
NA+glu within 1 minute of MUG overlay
NA+glu
minutes after MUG overlay
NA+glu
minutes after MUG overlay
NA+lac within 1 minute of MUG overlay
NA+lac
minutes after MUG overlay
NA+lac
minutes after MUG overlay
WT
H
J
K
* Record the degree of fluorescence as (-) or (+) or (++) or (+++). Where (-) is no fluorescence and (+++) is the greatest fluorescence.
5. Based on your experimental observations of each strain on EMB and the NA+lac and NA+glu plates decide on the genotype/phenotype of each of the strains and fill in the Table 3 below.
Strain
phenotype
(lac+ or lac-)
Genotype*
WT
lac+
lacZ+, lacI+, lacY+
H
lac+
lacZ+, lacI-, lacY+
J
lac-
lacZ+, lacI+, lacY-
K
lac-
lacZ-, lacI+, lacY+
* lacY- or lacY+, lacZ- or lacZ+, lacI- or lacI+ (put in genotype of all three genes for each strain) (2 marks)
6. In your own words, explain how the results you present in Tables 1 and 2 support the conclusions you present...
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