The lac operon consists of a promoter that initiates transcription of the gene i

Question

The lac operon consists of a promoter that initiates transcription of the gene i. which encodes a repressor protein. A separate promoter, p, within the operon initiates transcription of z, which encodes beta-galactosidase, and y, which encodes permease. The operator, o, where the repressor protein binds to inhibit transcription, is positioned between the promoter and the permease and beta-galactosidase genes. The superscript u denotes uninducible mutations, whereas superscript c denotes a constitutively active mutant. The table below describes the activity of beta-galactosidase and permease for haploid and diploid mutant strains. Match the dominant type of regulation controlling permease expression to each mutant strain, strain 1 strain 2 strain 3 strain 4 strain 5 strain 6

Explanation / Answer

strain1 cannot be determined.

Strain 2 is cis. Only one strand is there which has undergone mutation. (iu converted to i+)

strain 3 is trans. This is so because both the strands are i+, which means that inducer is produced. Under production of inducer, beta-galactosidase can be produced only when a factor acts in trans, and changes both the DNA strands.

strain 6 is cis. In this case, z+ has undegone cis mutation and has become z-.

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