During the last century, the scientific community made important discoveries that were key to deciphering the human genome. It was discovered that chromosomes are the basis of heredity; the double helix of DNA was observed for the first time; and the biological mechanism by which cells read the information contained in genes was established. This last discovery, along with major technological advances, gave rise to the new scientific field of genomics. Since then, thousands of genes and entire genomes have been sequenced.
Today, we have learned a great deal about genomics. We know more about whether a disease is hereditary and how it can affect us and our children. All of this began with the Human Genome Project, which laid the foundation for the application of genomics to medicine for both diagnosis and prevention.
What is a genome?
Before delving into the history and technology of the Human Genome Project, let's establish the basics of what a genome is and the enormous role it plays in personalized medicine.
We have explained that DNA is the chemical compound contained in all our cells and that it encodes all the instructions for creating and developing life. It is composed primarily of four nucleotides (among other molecules): Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). These bond together in a very specific way: A bonds with T, and C with G, forming a double helix or spiral staircase.
The complete set of DNA in an organism is called its genome. Simply put, the genome is the biological instruction manual for life, containing all the information necessary to develop, function, and reproduce. This code is passed from parents to offspring. The genome includes all genes, the basic units of genetics—fragments of DNA that carry out the information needed to produce proteins, which ultimately perform multiple functions in the organism.
The Human Genome Project
In 1990, the Human Genome Project (HGP) was launched with the goal of sequencing the vast majority of the human genome. This also meant discovering all human genes and locating them throughout the genome, as well as understanding the amount of coding DNA we have, thereby gaining knowledge about human development, physiology, medicine, and evolution. Ultimately, the goal was to advance biomedical research by deciphering important information about the workings of genetic material.
To achieve this goal, the International Human Genome Sequencing Consortium was formed, an open collaborative group involving twenty centers in six countries to sequence human DNA. Hundreds of scientists from 20 sequencing centers in China, France, Germany, the United Kingdom, and Japan participated in the consortium.
We might think this project involved sequencing the DNA of a single individual; however, it was carried out with the participation of numerous volunteers whose identities remain secret. The candidates were chosen from a diverse population who provided various blood samples. Not all the requested samples were used, so even the volunteers don't know whether their DNA was ultimately used for this project.
The Human Genome Project began in 1990 in the United States, with the official goal of mapping the complete DNA sequence of human beings.
Rightly considered one of the greatest research achievements in history, this analysis of the human genome was completed in April 2003. Mapping all the genes found was a huge challenge, which led to the allocation of vast sums of money to the project's completion. Initially, funding began at around $3 billion with an estimated completion time of 15 years. However, the project was completed two years ahead of schedule and with a lower overall budget.
The first draft of the human genome was published in 2000, with approximately 851,000,000 base pairs sequenced. In 2003, when the final results were published, it was revealed that the genome contained approximately 3 billion base pairs and that the total number of genes in the human organism was 20,000—astonishing when compared to the fact that small animals like rats have 30,000 genes! Therefore, the conclusion is that the complexity of an organism is not directly related to the number of genes it possesses.
Furthermore, the project scientists discovered that the percentage of DNA that codes for proteins is around 1.5%. This leads to the question of what the remaining 98.5%, known as non-coding DNA, does. Some research shows that some of this non-coding DNA is involved in gene regulation. But there are likely many other functions of non-coding DNA that we don't yet know about, and further studies are being conducted on these.
Human Genome Project Technology: How did it work?
In the mid-1970s, two sequencing methods were developed in parallel: the chemical sequencing method of Maxam and Gilbert and the enzymatic sequencing method, also known as the "chain termination method," of Sanger and Coulson. Both methods can determine the order of the nucleotides in a DNA fragment. Ultimately, the enzymatic method prevailed and, in fact, with some improvements, is still in use today.
The chain termination method is based on sequentially synthesizing a complementary DNA strand using special fluorescent nucleotides that halt synthesis. This produces fragments of varying sizes, each with a fluorescently labeled last nucleotide, allowing the DNA sequence to be determined using the information provided by all the different-sized fragments.
For the HGP, this sequencing technology was adapted to handle a huge amount of DNA material. The strategy used was called hierarchical shotgun sequencing, This involved many independent steps. First, large fragments of the human genome were cloned using bacterial artificial chromosomes (BACs). The human DNA was fragmented into pieces of about 150,000–200,000 base pairs each. These DNA fragments were then inserted into BACs and cloned into bacterial cells that replicated the human DNA fragments, yielding a sufficient quantity for sequencing. Once the DNA was replicated, the DNA sequences were randomly divided into smaller fragments for sequencing using the automated Sanger method.
Not only were the techniques important, but a lot of effort was also invested in developing specific computer programs that allowed the analysis of the sequenced data.
In total, the first complete sequencing of the human genome took more than 10 years and cost a lot of money in funding. At the end of the project, the researchers didn't stop: they continued to improve the techniques used, which ultimately led to Next-Generation Sequencing (NGS). This is how we can now sequence a person's genome quickly and affordably!
The Human Genome Project and Beyond
When the Human Genome Project began, the primary goal was to sequence the human genome. Thanks to the immense work carried out on this project, scientists succeeded in discovering the "instruction manual for life." This achievement represented a huge improvement in our understanding of human biology and was a major step forward for new genetic studies. Many genes related to inherited diseases have been mapped. This has paved the way for the development of new diagnostic methods and treatments, as well as for research to establish the genetic mechanisms involved in certain diseases.
New sequencing technologies are now available, allowing for faster and more affordable sequencing. This opens the door to personalized medicine; it allows us to know if we have a higher risk of developing certain diseases, which can also affect our offspring. It also helps us understand how we might react to specific drugs and much more information encoded in our genetic code. This is changing the concept of healthcare, providing tools to prevent disease in healthy individuals without any symptoms. Currently, this genomic revolution is improving medical checkups and, ultimately, potential treatments.
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