What is the Difference Between Mutation Rate and Substitution Rate

The key difference between mutation rate and substitution rate is that mutation rate is the frequency of occurrence of new mutations in a single gene based on deletions, insertions, or substitutions, while substitution rate is the rate of mutations that occur due to substitution of nucleotides in the DNA sequence.

Mutation is a common term in the avenue of molecular biology, genetics, and heredity. Mutation rate and substitution rate estimate the amount of genetic diversity and evolution rates in a particular lineage of organisms.

CONTENTS

1. Overview and Key Difference
2. What is Mutation Rate  
3. What is Substitution Rate
4. Similarities – Mutation Rate and Substitution Rate
5. Mutation Rate vs Substitution Rate in Tabular Form
6. Summary – Mutation Rate vs Substitution Rate

What is Mutation Rate?

Mutation rate is the frequency of new mutations in a single gene or an organism over time. It is not constant and is not limited to a single mutation type. Thus, various mutations are present. Mutation rates are specified for certain classes of mutations, such as point mutations that may occur due to insertions, deletions, and/or substitution of nucleotides. Point mutations are subject to changes in a single base, and missense and nonsense mutations are two subtypes of point mutations. There are several natural units of time for these mutation rates. They are characterized as mutations per base pair per cell division or per gene per generation, or per genome per generation.

The rate of mutation of an organism is usually evolved throughout and is influenced strongly by the genetics of each organism and the environment. When the mutation rate increases, health risks such as cancer and hereditary diseases in humans also increase. One way of determining mutation rate is the fluctuation test, which is also known as the Luria-Delbruck experiment. This method is important to mutation rates since it experimentally proves that mutation can occur without any selection.

Mutation rates vary between species and different regions. The human mutation rate in males (sperm) is higher than in females (egg cells). This shows that the human genome accumulates around 64 new mutations in order to generate gametes. The human mitochondrial DNA has a high mutation rate. The evolution theory of mutation rates identifies three principal forces, and they are the generation of more harmful mutations with higher mutation rates, the generation of more advantageous mutations with higher mutation rates and metabolic costs, and reduced replication rates in order to prevent mutation.

What is Substitution Rate?

Substitution rate is the most commonly measured class of mutation that is based on the substitution of nucleotides in a DNA sequence. They are easier to measure with standard DNA analysis. Substitution rates of mutations have different rates of mutation per generation than other classes of mutations which are frequently high. Many sites of a genome of an organism contain mutations with small fitness effects, and they are called neutral sites.

Mutations differ between species, and different rates of nucleotide substitutions are measured in substitutions. These are called fixed mutations and are measured in per base pair per generation. Fixed mutations are the changes that take place in a sequence of a gene without changing the proteins produced by that gene. These are usually used as estimates of the mutation rate. The substitution rate is calculated when the number of mutations in each generation is multiplied by the probability of the new mutation that reaches fixation.

What are the Similarities Between Mutation Rate and Substitution Rate?

• Mutation and substitution rates are important in population genetics.
• Moreover, both provide insight into genetic diversity.
• They also provide information on the evolution of populations.
• Both rates are calculated according to a specific formula.

What is the Difference Between Mutation Rate and Substitution Rate?

Mutation rate is the frequency of occurrence of new mutations in a single gene based on deletions, insertions, or substitutions, while substitution rate is the rate of mutations that occur due to the substitution of nucleotides in the DNA sequence. This is the key difference between mutation and substitution rate. Mutation rates estimate the amount of genetic diversity while substitution rates estimate the rate of evolution. Moreover, the formula for mutation rate is μ = m/N, where N is the average number of cells per culture, while formula for substitution rate is the number of new mutations in each generation (Nu) multiplied by the probability each new mutation reaches fixation (1/N), which equals u.

The following table summarizes the difference between mutation and substitution rate.

Summary – Mutation Rate vs Substitution Rate

Mutation and substitution rates are important parameters in genetic diversity. Mutation rate is the frequency of occurrence of new mutations in a single gene based on deletions, insertions, or substitutions, while substitution rate is the rate of mutations that occur due to the substitution of nucleotides in the DNA sequence. Mutation rates estimate the amount of genetic diversity, while substitution rate estimate the rate of evolution. This summarizes the difference between mutation rate and substitution rate.

Reference:

1. A;, Meyer S;vonHaeseler. “Identifying Site-Specific Substitution Rates.” Molecular Biology and Evolution, U.S. National Library of Medicine.
2. AS;, Peck KM;Lauring. “Complexities of Viral Mutation Rates.” Journal of Virology, U.S. National Library of Medicine.

Image Courtesy:

1. “ppat.1002950.g001” By Phylogeny Figures (CC BY 2.0) via Flickr
2. “Recent estimates of the human genome-wide mutation rate” By Aylwyn Scally – “The mutation rate in human evolution and demographic inference” Curr Opin Genet Dev. 2016 Aug 30;41:36-43. https://dx.doi.org/10.1101/061226 (CC BY 4.0) via Commons Wikimedia