What Is the Human Genome, and Why Is Sequencing So Important?

What Is the Human Genome, and Why Is Sequencing So Important?

A genome is an organism’s complete set of DNA, which stands for deoxyribonucleic acid. It is a chemical compound that contains the genetic instructions for every living organism.  DNA contains the genetic blueprint that dictates your personal traits, from blood type to height to hair color.

DNA molecules are composed of a pair of twisting strands. Each strand contains four chemical components, known as nucleotide bases. These bases are cytosine (C), guanine (G), adrenaline (A), and thymine (T). Nucleotide bases on opposite strands pair in a peculiar way: C always pairs with G and A always with T.

Each human genome is made up of approximately 3 billion such base pairs. They reside in the 23 pairs of chromosomes residing within the nucleus of each of our cells. Chromosomes contain hundreds and sometimes thousands of genes, each carrying instructions for making proteins. There are approximately 20,000 genes in the human genome, each of which makes an average of three proteins.

 

Timeline of events leading to the discovery of the human genome

The history of our understanding of the human genome goes back about 150 years, to the mid-19th century. The pace of discovery accelerated in the years after World War II, and the last 30 years have seen amazing advances in the field.

1860s: Gregor Mendel researches plant hybridization. Mendel is known as the father of modern genetics today.

1869: Friedrich Miescher identifies DNA with associated proteins (“nuclein”) from cell nuclei.

1952: Rosalind Franklin creates the famous “Photograph 51,” showing a distinctive pattern and illustrating DNA’s helix shape.

1953: Francis Crick and James Watson uncover the distinctive double helix structure of DNA.

1961: The genetic code for protein synthesis is cracked by Marshall Nirenberg.

1977: A rapid DNA sequencing technique is developed by Frederick Sanger.

1983: The first genetic disease (Huntington’s disease) is mapped.

1989: The gene mutation that causes cystic fibrosis is identified.

1990: Evidence for the existence of the BRCA1 gene, or Breast Cancer Gene 1, is presented. The gene produces a protein that suppresses tumor growth.

1990: The Human Genome Project is established to map the human genome.

1995: The first bacterium genome is sequenced (Haemophilus influenzae).

1996: The “Bermuda Principles” for free Human Genome Project data access are drafted.

1998: Celera Genomics Corporation is founded to sequence the human genome.

1999: The first human chromosome is decoded (chromosome 22).

2000: The genome sequence of a model organism (the fruit fly) is released.

2001: The first draft of the human genome is announced.

2002: The first mammal’s genome is decoded (a mouse).

2003: The Human Genome Project is completed, earlier than scheduled and under budget.

 

The Human Genome Project

The Human Genome Project consisted of a team of 32 scientists that was set up to complete sequencing of the genome. The project revealed that there are somewhere in the order of 20,000 human genes—far fewer than previous estimates of 50,000 and higher. The findings of the Human Genome Project have ultimately given the world detailed information on the structure, function, and organization of a complete set of human genes, providing information on the basic blueprint for the function and development of a human being.

 

The project is announced to the world

This groundbreaking scientific undertaking was announced on June 25, 2000, by US President Bill Clinton, with British Prime Minister Tony Blair present via satellite link. Also present were representatives from Japan, Germany, and France, countries which, along with China, contributed greatly to the project.

Clinton hailed the undertaking as the most important, wondrous map ever produced by humankind. Genome science, he said, would go on to have a very real impact on all of our lives, and even more, upon the lives of our children. He also predicted that the findings made during the course of the project would revolutionize disease diagnosis and treatment, and even facilitate prevention.

 

Why is genome sequencing such a significant breakthrough?

Upon the first publication of the majority of the genome in 2001, Francis Collins, director of the National Human Genome Research Institute, explained that the genome should be thought of in terms of a book with multiple uses. In part, it is a history book providing a narrative of human evolution through time. It is also a shop manual, providing a detailed set of instructions for creating every human cell. Perhaps most significantly, the genome is a medical textbook, providing insights that can bestow immense powers upon health care providers in treating, preventing, and potentially curing genetic diseases.

The practical benefits of genome sequencing were evident in a recent study at Rady Children’s Hospital in San Diego, California. The study revealed that sequencing the whole genome of infants diagnosed with a rare disease led to shorter hospital stays and better health outcomes overall. Shimul Chowdhury, director of the hospital’s clinical laboratory, presented data on six case studies of infants in the neonatal intensive care unit, illustrating how sequencing their whole genomes led to faster, more accurate diagnoses, which in turn enabled medical professionals to better estimate prognosis and provide treatment plans faster. Not only that, but rapid whole genome sequencing led to a reduction in costs associated with treating the babies, somewhere in the order of $1.8 million. Chowdhury stated that his group was in talks with multiple children’s hospitals in the hope of rolling out whole genome sequencing for infants across the US.