Scientists had published the map of the human genome for the first time nearly two decades ago which was hailed as a breakthrough.
What is Genome in Simple Definition?
Genome represents the complete hereditary information of an organism encoded in its DNA. Genome comprises both the genes and the non-coding sequences of the DNA. It covers the entire gamut of building, running, maintaining an organism and passing life on to next generation. The word Genome was coined for the first time by Hans Winkler. He was working as a professor of Botany at the University of Hamburg in Germany.
What is a Genome Made of?
In almost all living things on earth, genome is made of a chemical called DNA. The Genome contains genes which affect the characteristics of the living organism. Genome contains chromosome, these chromosomes contain genes, and these genes are made up of DNA. All living things are made of different unique genomes. Humans, animals, birds, all have different genomes, and no two humans have the same genome. The difference in the genome between 2 people is smaller than the genome difference between a human and a chimpanzee.
How Many Genomes do Humans have?
Human genome comprises of 23 chromosome pairs with a total of 3 billion DNA base pairs. There are 24 different types of human chromosomes, out of these 22 are autosomal chromosomes in addition there are X and Y Chromosomes that determines the sex. The number of human protein-coding genes are estimated to be in the range of 20,000 – 25,000. As the genome sequencing quality and gene finding methodologies have kept improving over time, the estimated number of genes in human body has been steadily decreasing from initial predictions of 1,00,000 and above.
What is DNA?
DNA stands for Deoxyribonucleic acid (DNA). It is a molecule which is made up of biological instructions which result in the uniqueness of each species. DNA is passed from adult organisms to their offspring at the time of reproduction.
A gene is a part of a DNA molecule.
Hereditary element of genetic information.
Encodes proteins synthesis
Length is about a few hundreds of bases
A Higher organism has about thousands of genes
Variations of the gene named alleles can be naturally selected
The genome is the total DNA in a cell
All set of nuclear DNA
Encodes both proteins and regulatory elements for proteins synthesis
Length of the genome of a higher organism is about billion base pairs
Each organism has only one genome
Horizontal gene transfer & duplication cause large variations in the genome
The Human Genome Project
- As early as the 1980s, momentum was gathering behind activities that supported, and would eventually define, the Human Genome Project.
- Conversations had turned into workshops that likened characterization of the human genome to characterization of the human anatomy that had centuries earlier revolutionized the practice of medicine.
- In 1990, with continued support from the US and widespread international collaboration and cooperation, the $3 billion dollar Human Genome Project was launched.
- The project aimed to determine the sequence of the human genome within 15 years.
- By 2000 (well ahead of schedule) a working draft of the human genome was announced.
- This was followed by regular updates and refinements and today we all have access to a human “reference genome sequence”.
Why did it take 20 years?
- Much of the newly sequenced material is the “heterochromatic” part of the genome.
- This is more “tightly packed” than the euchromatic genome and contains many highly repetitive sequences that are very challenging to read accurately.
- These regions were once thought not to contain any important genetic information but they are now known to contain genes that are involved in fundamentally important processes such as the formation of organs during embryonic development.
- Among the 200 million newly sequenced base pairs are an estimated 115 genes predicted to be involved in producing proteins.
Two key factors made the completion of the human genome possible:
- Choosing a very special cell type
- The new sequence was created using human cells derived from a very rare type of tissue called a complete hydatidiform mole, which occurs when a fertilized egg loses all the genetic material contributed to it by the mother.
- Most cells contain two copies of each chromosome, one from each parent and each parent’s chromosome contributing a different DNA sequence.
- A cell from a complete hydatidiform mole has two copies of the father’s chromosomes only, and the genetic sequence of each pair of chromosomes is identical.
- This makes the full genome sequence much easier to piece together.
- Advances in sequencing technology
- A new method called “shotgun sequencing”, involved breaking the genome into very small fragments of about 200 base pairs, cloning them inside bacteria, deciphering their sequences, and then piecing them back together like a giant jigsaw.
- This was the main reason the original draft covered only the euchromatic regions of the genome — only these regions could be reliably sequenced using this method.
- The latest sequence was deduced using two complementary new DNA-sequencing technologies.
Is the genome now completely sequenced?
- Well, no. An obvious omission is the Y chromosome, because the complete hydatidiform mole cells used to compile this sequence contained two identical copies of the X chromosome.
- However, this work is underway and the researchers anticipate their method can also accurately sequence the Y chromosome, despite it having highly repetitive sequences.
- Even though sequencing the (almost) complete genome of a human cell is an extremely impressive landmark, it is just one of several crucial steps towards fully understanding humans’ genetic diversity.
Applications & Benefits of Human Genome Project
It can help us
- understand diseases including genotyping of specific viruses to direct appropriate treatment,
- in the identification of mutations linked to different forms of cancer,
- understand the design of medication & more accurate prediction of their effects,
- in the advancement of forensic applied sciences, biofuels, animal husbandry, etc.
- understand evolution much more accurately.
- Another proposed benefit is the commercial development of genomics research related to DNA based products, a multibillion-dollar industry.
Genome India Project
- Taking inspiration from the Human Genome Project, the Department of Biotechnology (DBT) initiated the ambitious Genome India Project” (GIP) in 2020.
- It aims to collect 10,000 genetic samples from citizens across India, to build a reference genome.
- Gene Mapping project involves 20 leading institutions of the country with the Centre for Brain Research of Indian Institute of Science (IISc) Bangalore as the nodal point.
IndiGen: India’s Genome Sequencing Project
- The Council of Scientific and Industrial Research (CSIR) concluded the six-month-long exercise of conducting a “whole-genome sequence” of a 1,008 Indians that beloged to diverse ethnicities.
- The project is part of a programme called “IndiGen” and is a precursor to Genome India Project” (GIP).
- The project involved the Hyderabad-based Centre for Cellular and Molecular Biology (CCMB) and the CSIR-Institute of Genomics and Integrative Biology (IGIB).
Source: Indian Express