Understanding a human pangenome map

Source: The post is based on the article “Understanding a human pangenome map” published in The Hindu on 22^nd May 2023.

Syllabus: GS 3 – Science and Technology

News: A pangenome reference map has been built using genomes from 47 anonymous individuals from Africa, the Caribbean, Americas, East Asia, and Europe. The article explains its relevance.

What is genome and genome sequencing?

Read Here: Explained: The complete human genome, and what it tells us and Genome sequencing

The genome is an identity card like Aadhaar, which is unique for every individual.

What is a reference genome?

When genomes are newly sequenced, they are compared to a reference map called a reference genome. This helps to understand the regions of differences between the newly sequenced genome and the reference genome.

Reference genome was first built in 2001. It helped scientists discover thousands of genes linked to various diseases and better understand diseases like cancer at the genetic level and design novel diagnostic tests.

However, the reference genome had many gaps and errors. It was also not representative of all human beings as it was built using mostly the genome of a single individual of mixed African and European ancestry.

Therefore, to address these gaps and errors, scientists have developed the pangenome map.

What is a pangenome map?

The pangenome is a graph unlike the earlier reference genome which was a linear sequence. 

The graph of each chromosome resembles a bamboo stem, with nodes where sequences from all 47 individuals come together, indicating similarity.

The internodes, which have different lengths, represent genetic variations among individuals from different ancestries.

The researchers used long-read DNA sequencing technologies to create complete and contiguous chromosome maps in the pangenome project.

Longer reads technology helps to assemble the sequences with minimum errors and read through the repetitive regions of the chromosomes which are hard to sequence with short-read technologies used earlier.

However, even though pangenome map is error free, it does not represent all of human diversity.

Why is a pangenome map important?

Even though two humans are more than 99% similar in their DNA, there is still about a 0.4% difference between them.

Hence, a complete and error-free human pangenome map will help understand these differences and explain human diversity better.

It will also help understand genetic variants in some populations, which result in underlying health conditions.

The present map does not contain Indian genome sequences. However, it will help in mapping Indian genomes against the error-free and full reference genomes known till date.

Future pangenome maps incorporating high-quality genomes from diverse Indian populations, including endogamous and isolated groups, will provide insights into disease prevalence, facilitate the identification of new genes associated with rare diseases, and aid in the discovery of novel drugs to combat these diseases.