Genetics and Genomics

Free Version

Upgrade subject to access all content


Complemention in a Bacterial Operon


Bacteria are considered haploid as their genome is made of a single circular chromosome. However, bacteria can contain small circular pieces of DNA called plasmids. Often a plasmid can contain new genes not found in the bacterial genome, but they may also contain additional copies of genes found in the genome. In this way, a mutation in an operon would be complemented by another copy of the operon on a plasmid.

For the following question, ​the plasmid contains the entire lac operon, including lacI, the gene which codes for the lac repressor. Determine what the effect would be for genomic and plasmid copies of the lac operon under these conditions:

In the genome of the bacterial cell, the sequence of the promoter region has been altered such that it is no longer recognized. This would cause the genomic lac genes to be


In the lac operon on the plasmid, the lacI gene is non-functional. If the genomic copy was not present, the lac genes on the plasmid would be


With both copies present in the cell the proteins of the lac operon are