Human Pangenome Map

Context: 

A new study published in the Nature journal describes a pangenome reference map, built using genomes from 47 anonymous individuals (19 men and 28 women).

What is a genome? 

• The genome is the blueprint of life, a collection of all the genes and the regions between the genes contained in our 23 pairs of chromosomes. 
• Each chromosome is a contiguous stretch of DNA string. In other words, our genome consists of 23 different strings, each composed of millions of individual building blocks called nucleotides or bases. 
• The four types of building blocks (A, T, G and C) are arranged and repeated millions of times in different combinations to make all of our 23 chromosomes. 
• Genome sequencing is the method used to determine the precise order of the four letters and how they are arranged in chromosomes. 
• Sequencing individual genomes helps us understand human diversity at the genetic level and how prone we are to certain diseases.
• The genome is an identity card like Aadhaar. As each of our Aadhar card is unique, so is our genome. 

What is a reference genome? 

• When genomes are newly sequenced, they are compared to a reference map called a reference genome. 
  • This helps us to understand the regions of differences between the newly sequenced genome and the reference genome.
• The first reference genome was made in 2001. It helped scientists discover thousands of genes linked to various diseases; better understand diseases like cancer at the genetic level; and design novel diagnostic tests. 
• The reference genome of 2001 was 92% complete and contained many gaps and errors.
• It was not representative of all human beings as it was built using mostly the genome of a single individual of mixed African and European ancestry.

About Pangenome Map:

• The pangenome is a graph unlike the reference genome, which is a linear sequence.
• The graph of each chromosome is like a bamboo stem with nodes where a stretch of sequences of all 47 individuals converge, and with internodes of varying lengths representing genetic variations among those individuals from different ancestries.

Importance of Pangenome Map:

• Although any two humans are more than 99% similar in their DNA, there is still about a 0.4% difference between any two individuals. 
• This may be a small percentage, but considering that the human genome consists of 3.2 billion individual nucleotides, the difference between any two individuals is a whopping 12.8 million nucleotides. 
• A complete and error-­free human pangenome map will help us understand those differences and explain human diversity better. 
• It will also help us understand genetic variants in some populations, which result in underlying health conditions. 
• The pangenome reference map has added nearly 119 million new letters to the existing genome map and has already aided the discovery of 150 new genes linked to autism.

Limitation of the map

• Genomes from more people from Africa, the Indian sub­continent, indigenous groups in Asia and Oceania, and West Asian regions are not represented in the current version of the pangenome map.

News Source: The Hindu