FC0 is a (+) frameshift mutation in the rII locus. A stock of FC0 is mutagenized with proflavin and plated on a lawn of E. coli K, where only phenotypically wild type phage can grow. You pick one of the plaques and make a stock of it. You would like to determine whether the stocks reversion to rII+ was a true reversion or the result of a second site suppressor mutation. To do this you cross the phage with phage from a wild type stock and plate the progeny on E. coli B. You find that 96% of the plaques are small and 4% large. Based on this data, you conclude that the stocks reversion to rII+ was the result of:__________
A. true reversion.
B. second site suppressing mutation

The second site of the repression mutation as 96 percent showed the small colonies that tells the growth was not the good as the agar that allowed the growth of the only wild type of strains. So it was not a true reversion to a wild type.

And because the small colony is visible, it means that there are some growth which means that some of the strains tried to turn back in the wild type.

Histrionicus Histrionicus · Answer 2 · 2021-12-15T06:38:56+01:00

Based on this data, you conclude that the stock's reversion to rII+ was the result of - B. second site suppressing mutation.

The second site mutation

a double mutation within a gene.
normally the second-site mutation suppresses the first mutation so that the double mutant has the wild-type phenotype.

True reversion

A mutation that precisely restores a mutant DNA sequence to the wild-type DNA sequence

here in this case there is already a frameshift mutation present and mutagenized with proflavin and plated on a lawn of E. coli K.

we know these plate plates only allow phenotypically wild-type phages to grow.
here just 96% showed small colonies which indicate second site suppressing mutation
it shows that growth was not that brilliant as the agar allowed the growth of only wild-type strains, therefore, it was not a true reversion to the wild type.
And since a small colony was visible means there was some growth meaning some strains tried to turn back to the wild type.

Thus, Based on this data, you conclude that the stocks reversion to rII+ was the result of: B. second site suppressing mutation.

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