Question

You discover an organism with a new mutation in the gene that you are studying that changes the codon in the mRNA from a GCC (Ala) to a GAC (Asp) causing a mutant phenotype. You feed this organism a mutagen and find that in one of its progeny the phenotype has now reverted back to wild-type. When you look at your gene in this offspring you find the mutation GAC (Asp) has been changed back to the original GCC (Ala). This is an example of

	a.	Intragenic suppression
	b.	Intergenic suppression
	c.	Frameshift mutation
	d.	Reverse mutation
	e.	None of the above

Answer 1

Ans - Above given case is of Reverse mutation.

* Wild type phenotype can be restored by various ways :

* One way is by Making the nucleotide changes on the original site , mutated by  forward mutation , thus reverting the mutation and restoring the wild phenotype - Reverse mutation.

* True reversion is the reversal of the original nucleotide change. (As in the given case)

* Second way, mutations at the second site other than the primary forward mutation can also revert the wild type phenotype by suppressing the effect of forward mutation.

*Intragenic mutation - when the  second mutation within a mutant gene that results in an apparent restoration of the original phenotype.

* Intergenic mutation - when the second mutation is within the other gene (not in the original gene) but results in restoration of original phenotype.

* In the above case  there is restoration of the original nucleotide change, thus it is an example of Reverse mutation.