Difference Between Forward and Reverse Mutation

The key difference between forward and reverse mutation is that forward mutation is the mutation that alters the phenotype from wild type to mutant while reverse mutation is the mutation that alters the phenotype from mutant to wild type.

A mutation is an alteration of the nucleotide sequence of a gene or a genome. Mutation can happen in somatic cells or germline cells. Germline mutations pass from parents to offspring, while somatic mutations do not pass into the next generations. Moreover, if we consider a locus with two alleles, mutations can be forward or reverse mutations. A forward mutation is a mutation that changes wild type allele to a detrimental allele. In contrast, reverse mutation changes the already changed allele (mutant) to a wild type allele, reversing the forward mutation.

CONTENTS

1. Overview and Key Difference
2. What is Forward Mutation
3. What is Reverse Mutation
4. Similarities Between Forward and Reverse Mutation
5. Side by Side Comparison – Forward vs Reverse Mutation in Tabular Form
6. Summary

What is Forward Mutation?

Forward mutation is the mutation that changes wild type allele into a detrimental allele. The common phenotype seen in natural population is usually called a wild type phenotype. When it alters into a mutant or a different phenotype, it is called forward mutation. Forward mutation confers a different phenotype than wild type phenotype.

A forward mutation takes place in the lacZ gene in E. coli, inactivates the gene and makes it unable to grow in a medium containing lactose. Reverse mutation makes the bacterium capable of growing in the same medium containing lactose. Though there are mutations, the rate of forward mutation is very low, and it is around 10^-8 per generations.

What is Reverse Mutation?

Reverse mutation, also called backward mutation, is the mutation that reverses the forward mutation. In other words, it is the mutation that changes mutant into wild type allele or phenotype. Thus, reverse mutation converts the aberrant state of a gene back to the normal or wild type state.

When the original nucleotide sequence of the gene is restored by the reverse mutation, it is known as a true revertant, but, it occurs rarely. However, it restores the normal function of the gene, the normal protein or the normal phenotype. In many reverse mutations, the phenotype is reversed into the wild type phenotype. Moreover, reverse mutations are likely to occur at a lower rate than forward mutations. In genetics, reverse mutation tests are useful in identifying DNA repair genes.

What are the Similarities Between Forward and Reverse Mutation?

• Forward and reverse mutations are two types of mutations.
• Both types alter the nucleotide sequence of a gene or a genome.

What is the Difference Between Forward and Reverse Mutation?

Forward mutation is a mutation that results in a different phenotype than the wild type phenotype. In contrast, the reverse mutation is a mutation that restores the wild type phenotype from the mutant phenotype. So, this is the key difference between forward and reverse mutation. Reverse mutations are useful in identifying DNA repair genes, unlike forward mutations.

Moreover, another difference between forward and reverse mutation is the rate of mutation. Reverse mutations are likely to occur at a lower rate than forward mutations.

Summary – Forward vs Reverse Mutation

Forward mutation is a mutation that confers a phenotype different from that conferred by the wild-type gene. In contrast, the reverse mutation is a mutation that restores the wild-type phenotype by reversing the forward mutation. Therefore, reverse mutations undo the effects of forward mutations. So, this is the key difference between forward and reverse mutation. However, the reverse mutation rate is extremely low compared to the forward mutation rate.

Reference:

1. Robinson, Arthur, and Anthony J.F. Griffiths. “Mechanisms of Mutation.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 11 Oct. 2019, Available here.
2. “Revertant.” Revertant – an Overview | ScienceDirect Topics, Available here.

Image Courtesy:

1. “Forward mutagenesis” By © 2014 Lena M. Kutscher and Shai Shaham. – Kutscher L. M., Shaham S. Forward and reverse mutagenesis in C. elegans (January 17, 2014), WormBook, ed. The C. elegans Research Community, WormBook, doi/10.1895/wormbook.1.167.1 (CC BY-SA 2.5) via Commons Wikimedia