A mutant strain of E. coli is found that produces both beta-galactosidase and pe

Question

A mutant strain of E. coli is found that produces both beta-galactosidase and permease at high levels whether lactose is present or not.

(a) What are two possible genotypes for this mutant?

Another mutant is isolated that produces no beta-galactosidase at any time but produces permease if lactose is present in the medium. A merodiploid strain is formed from these two mutants. in the absence of lactose, neither beta-galactosidase nor permease is made. When lactose is added, the merodiploid strain makes both beta-galactosidase and permease.

(b) What is the genotype of the merodiploid strain?

Explanation / Answer

A mutant of E. coli is found that produces both beta - galactosidase and permease at high levels in the presence or absence of lactose

a) The two possible genotypes for this mutant is given as-:

F+ Z+ Y+

Now another mutant is isolated that produces no beta-galactosidase at any time but produces permease if lactose is present in the medium.

The genotype for this mutant is given as-:

F- Z- Y-

Given a merodiploid strain is formed from these two mutants.

Merodiploid is partially diploid bacterium having its own chromosome and a fragment that is introduced either by conjugation, transformation or transduction. It is given by-:

F+ Z+ Y+ x F- Z- Y-

=F' Z+ - Y-

b) The genotype for the merodiploid strain is F' Z+ - Y-

For Merodiploid strain in the absence of lactose, neither beta-galactosidase nor permease is formed but in the presence of lactose both beta-galactosidase and permease is produce.

As mutant 1 have the ability to make beta-galactosidase in the absence or presence of lactose but the mutant 2 is unable to make beta-galactosidase at any time so in the new mutant the gene for beta galactosidase is expressed only in the presence of lactose.

Also the permease producing gene of 2 mutant is dominant that is the reason the merodiploid strain produces permease in the presence of lactose but not in the absence of lactose.

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