Difference Between Whole Genome Sequencing and Exome Sequencing

The key difference between whole genome sequencing and exome sequencing is that the whole genome sequencing sequences the entire genome of an organism while the exome sequencing sequences only the exome or the protein-coding genes of an organism.

Sequencing is a technique that determines the precise order of the nucleotides in a particular DNA molecule. It merely reflects the correct order of the four bases; adenine (A), guanine (G), cytosine (C) and thymine (T) in a DNA fragment. There are several sequencing methods such as Sanger sequencing, next-generation sequencing, etc. Furthermore, either the complete genome of an organism (whole genome sequencing) or only the protein-coding genes in the genome (exome sequencing) can undergo sequencing.

CONTENTS

1. Overview and Key Difference
2. What is Whole Genome Sequencing
3. What is Exome Sequencing
4. Similarities Between Whole Genome Sequencing and Exome Sequencing
5. Side by Side Comparison – Whole Genome Sequencing vs Exome Sequencing in Tabular Form
6. Summary

What is Whole Genome Sequencing?

The human genome contains almost three billion base pairs of DNA. The whole genome sequencing is a method that sequences the complete genome of an organism. Therefore, in whole genome sequencing, the consideration is on the entire collection of DNA molecules including exomes, introns, intergenic spaces, etc. Moreover, the whole genome sequencing sequences not only the genome that resides inside the nucleus but also the mitochondrial DNA as well.

In preparing for this sequencing, the first step is to extract the whole DNA. Then, the extracted DNA undergoes the sequencing procedure using a suitable sequencing method. By analysing the resulting sequences, utilising a bioinformatics tool, we can find out the rare diseases, cancer, infectious diseases, etc.

What is Exome Sequencing?

Exome is a part of the genome that contains about 1.5% of the genome, and it is the collection of exons. Exons are the sequences that transcribe into mRNA and then to the final protein product. Hence, exome sequencing sequences the entire protein-coding sequences in the genome. Exome sequencing reveals the genetic disorders since most of the genetic disorders arise due to the mutations of the protein-coding genes. Hence, diagnostic processes of genetic disorders frequently use exome sequencing as a method to diagnose the disease. Also, when comparing with the whole genome sequencing application for genetic testing, the exome sequencing takes less time to employ and is less expensive.

In exome sequencing, first, it is necessary to select only the protein coding sequences from the total DNA. Note that the humans have about 180000 protein-coding sequences. Then, the exome is sequenced using a high throughput sequencing method.

What are the Similarities Between Whole Genome Sequencing and Exome Sequencing?

• Whole Genome Sequencing and Exome Sequencing are two applications of sequencing.
• Both methods are useful in determining the correct order of the nucleotide sequence in both methods.
• Also, bioinformatics helps in both techniques to analyse data.

What is the Difference Between Whole Genome Sequencing and Exome Sequencing?

Whole genome sequencing sequences the entire DNA of the genome of an organism, while the exome sequencing sequences only the protein coding sequences from the genome. Therefore, this is the fundamental difference between whole genome sequencing and exome sequencing. Also, though both methods are widely in use to determine the correct order of the nucleotide sequence, the whole genome sequencing is costly and time-consuming than the exome sequencing.

The below infographic tabulates the difference between whole genome sequencing and exome sequencing.

Summary – Whole Genome Sequencing vs Exome Sequencing

Sequencing reveals the precise order of the bases in a DNA fragment and it can be either whole genome sequencing or exome sequencing. Here, the whole genome sequencing sequences the complete genome of an organism while the exome sequencing sequences only the protein-coding sequences in the genome. Considering their applications, the whole genome sequencing is helpful in analysing the genetic aberrations such as single nucleotide variations, deletions, insertions, etc. in whole genome while the exome sequencing is helpful in detecting the genetic diseases. Therefore, this is the difference between whole genome sequencing and exome sequencing.

Reference:

1.“Whole-Genome vs. Whole-Exome Sequencing vs. Targeted Sequencing Panels.” Healio, SLACK Incorporated. Available here  
2.“What Are Whole Exome Sequencing and Whole Genome Sequencing? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health. Available here  

Image Courtesy:

1.”Whole genome shotgun sequencing versus Hierarchical shotgun sequencing”By Commins, J., Toft, C., Fares, M. A. – “Computational Biology Methods and Their Application to the Comparative Genomics of Endocellular Symbiotic Bacteria of Insects.” (CC BY-SA 2.5) via Commons Wikimedia  
2.”Exome Sequencing Workflow 1a”By SarahKusala – Own work, (CC BY 3.0) via Commons Wikimedia