Question

It would be appreciated if someone could help explain this question to me. Thanks a lot!

-88.)A strain of E. coli is genetically engineered in which the lacZ and lacY genes are removed and replaced with a gene encoding a fluorescent protein. A copy of the operon in which the protein product fluoresces green is inserted into the chromosome, and a copy in which the protein product fluoresces red is inserted into a plasmid. Both copies carry a wild-type lacO gene, and the cells of the strain have a single copy of the lacl repressor gene. If both fluorescent proteins are expressed the cells fluoresce yellow (because a combination of red and green fluorescence appears as yellow), and if neither of the fluorescent proteins is expressed, the cells show no fluorescence. If the lacl gene in the genetically engineered fluorescent strain were nonmutant but the laco sequence on the chromosome mutated to lacOc, how would the cells fluoresce in the presence of inducer? In the absence of inducer? a. yellow; red b. yellow; yellow yellow; no fluorescence d. None of the other answer options is correct e. yellow; green Suromasns plend C. yelloa Sopes

Answer 1

Let's first consider the given statement :

• Lac Z and Y genes replaced by GFP and RFP (Red fluorescent protein encoding gene).
• GFP gene is inserted in bacterial chromosome and RFP gene is inserted into plasmid .
• Both copies of operon carry lac O gene or operator gene which gets bound by repressor from I gene .
• Lac O gets mutated to Lac O^{​​​​​​c} because of which inducer can not bind to it and can not switch off transcription of GFP in chromosomal copy of operan so green light is generated in presence of inducer which can bind to repressor .RFP is normally expressed and gives red color fluorescence.Net result is yellow light.
• In absence of inducer no effect on GFP gene as operator is mutated to stop any inhibitory effect of repressor . So here also both red and green lights on mixing produced yellow color .

Correct answer is( b) yellow ; yellow