Difference between Whole Genome Sequencing and Exome Sequencing

The process of finding out the order of nucleotides in DNA strands is known as genome or DNA sequencing. Sequencing an organism’s genome helps to study genetic aberrations and anomalies. Frederick Sanger developed a novel technique of sequencing in 1977 that brought about a leap in the world of bioscience. However, this technique was expensive and time-consuming.

New technology for rapid DNA sequencing was then developed, that is referred to as next generation sequencing (NGS). Whole genome sequencing (WGS) and whole exome sequencing (WES) are two methods in next generation sequencing that are being used widely in healthcare to study genetic variations.

Steps of Genome Sequencing

  • DNA Cutting: This step involves cutting DNA into small pieces by treating it with restriction enzymes.
  • DNA Tagging: The short DNA fragments are tagged with probes for identification in later stages.
  • Sequencing: The tagged DNA fragments are added into the sequencer along with the reagents and chemicals required.
  • Analysis: The dataset generated can be analysed through various bioinformatic techniques.

Refer: Genome, Genome Sequencing, And Applications

Whole Genome Sequencing

Whole genome sequencing (WGS), also called full genome sequencing or complete genome sequencing is the method of sequencing the entire genome of an organism. It involves all the coding and non-coding regions along with the mitochondrial and chloroplast genome.

It can be used to study genetic rearrangements and anomalies in both coding and non-coding regions. However, sequencing of the entire genome is expensive and time-consuming. It creates a data set that is very large for the bioinformaticians to process.

Exome Sequencing

A gene is composed of exons (coding regions) and introns (non-coding regions). All the exons combined in a genome are referred to as exomes. The exomes make about 1-2% of the entire organism’s genome. The sequencing of these exomes is referred to as exome sequencing or whole exome sequencing (WES).

In comparison to WGS, only 1-2% of the whole genome is sequenced. Only the coding regions are sequences that can be studied to find out genetic variations. This process is inexpensive and quicker. It does not generate large data sets like WGS.

However, WES falls short when there are anomalies in non-coding sequences. Whole genome sequencing has the advantage of sequencing even the non-coding regions, which are sometimes responsible for genetic disorders.

Whole Genome vs Exome Sequencing

Whole Genome Sequencing

Exome Sequencing

Definition

The process of sequencing the whole genome of an organism is referred to as whole genome sequencing.

The process of sequencing exomes of an organism is referred to as exome sequencing.

Sequences

All the coding, non-coding, mitochondrial and chloroplast (in plants) genomes are sequenced.

Only the coding genome (exons) are sequenced.

Time Taken

It is a time-consuming process.

It is comparatively less time-consuming.

Cost

It is costlier.

It is cheaper.

Sequence Database

The sequence database generated is very large and sometimes is incomprehensible.

The sequence database generated is comparatively smaller.

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Frequently Asked Questions

Is whole genome sequencing better than whole exome sequencing?

Whole exome sequencing is better than whole genome sequencing if you are looking to sequence only coding regions, because it is more sensitive towards detecting mutations.

Why is whole genome sequencing important?

Whole genome sequencing is important to study the whole genome for detecting any lethal changes in the genes, and it also helps to study the progression of cancer.

State one application of whole exome sequencing.

Whole exome sequencing is being used by parents who are expecting a child, to find out mutations in the coding part of the foetus.

What are the risks of whole genome sequencing?

Genome sequencing can sometimes lead to the knowledge of unnecessary information to the patient that leads to expensive tests and treatments which brings stress and anxiety.

What is rapid whole genome sequencing?

Rapid whole genome sequencing (rWGS) is an emerging technique that sequences neonatal genomes in time for ICU treatment. This technique is still under process and needs to be tested on critically ill newborns.

What is the most challenging issue facing genome sequencing?

  • Limited resources
  • Time and cost
  • Unawareness among humans and
  • Ethical questions.

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