History - as it was conceived a few years ago

A retrospective overview

A revolution in the post-genome era

Today we are on the eve of a new and challenging epoch in science. It is often refer to as “the post-genome era”, indicating that the focus has shifted from describing the genome to making practical use of all the new information we have gained. By applying experimental methods to the rapidly growing body of sequence information, functions will be assigned to the unknown gene products discovered. During the post-genome era we will experience a revolution in the way cells, cellular processes, organisms and diseases are studied.

The road to the post-genome era has been long and winding, but the scientists have fought their way along it at an increasingly rapid pace.

Understanding inheritance and describing the DNA-molecule

Genetics is a relatively new branch of science. In the middle of the 19th century, Mendel suggested that inheritance is determined by factors that can be inherited independently of each other. He also understood that recombining these factors resulted in variations in the offspring; variations conformable to laws.

In 1953 Watson and Crick described the structure of the DNA-molecule. This breakthrough is often regarded as the discovery of the century. It launched the area “molecular genetics”, i.e. investigations on the structure and function of genes on a molecular level.

Technology crucial to advances in science

A step forward for modern gene technology was accomplished in 1970, when scientists managed to isolate an enzyme that could recognise a sequence in the DNA-molecule and split the DNA-molecule at that specific sequence. During the mid-seventies the Southern-blot method became available for separating DNA-fragments of different sizes by a filterhybridization technique. Ten years later the PCR (polymerase chain reaction) method was introduced for fast and easy manufacturing of copies of DNA fragments. By PCR millions or billions of copies can be generated, allowing studies of minimal biological specimens. An example, which has revolutionized forensic medicine, is that detailed information about an individual’s DNA can be obtained from a single hair.

The Human Genome Project

In 1990, a prominent international cooperation started. This Human Genome Project (HGP) has been the prime mover for producing complete blueprints of several living organisms. At the start, the intention was to complete the project in 15 years by discovering all of the human genome and make it accessible for further biological study. Also, HGP aimed at determining the complete sequence of the chemical base pairs that make up human DNA. In 1990, scientists were far from convinced that the project would be feasible. For example, considerable technical development had to be accomplished to meet with the goals of the project.

Looking back, HGP has surpassed all expectations. The early phase of the HGP was characterized by efforts to create the biological, instrumentation, and computing resources necessary for efficient production-scale DNA sequencing. The project has collected DNA samples from volunteers around the world, representing a mix of people of both sexes and many ethnic and geographical backgrounds. Today, several types of genome maps have been completed. Thanks to a remarkable technological progress, a rough working draft of the entire human genome sequence was completed in June 2000, with analyses published in February 2001. Efforts are still underway to complete the finished, high-quality sequence. Since the start in 1990, the ultimate goal of HGP is still to obtain a complete and highly accurate reference sequence that is largely continuous across each human chromosome.

A methodology to handle loads of information

Over the more than ten years of operating, HGP has generated enormous amounts of information. To manage all this information, a new branch of science has evolved. It is called bioinformatics, and involves the application of computer and statistical techniques to the management of information. In genome projects, informatics includes the development of methods to search databases quickly, to analyse DNA sequence information, and to predict protein sequence and structure from DNA sequence data. An important bioinformatic task has been to develop algorithms for comparing and interpreting sequence information. To build up databases and analytical tools for modelling complex biological networks and interactions are other important responsibilities for bioinformaticians.

Using mRNA for an alternative sequencing strategy

An alternative strategy for sequencing was presented during the early 90ties by Craig Venter, the founder of the biotechnological company Celera. The functional portion of the human DNA supposedly accounts for less than 10% (perhaps less than 5%) of the entire human genome. In other words, genes are slotted in between sections of so-called non-coding DNA whose function we do not understand. The HGP strategy, i.e. sequencing everything, could be considered as lavishness with resources since the main part of the information lacks relevance. The scope of the strategy by Venter and co-workers is to focus the investigations to messenger ribonucleic acid (mRNA) instead of DNA. mRNA is a transient intermediary molecule, which serves as a template for protein synthesis in the cell. The point of using mRNA is that it does not include any non-coding DNA. The mRNA molecule can be isolated and used as a template to synthesize a complementary DNA (cDNA) strand, which can then be used to locate the corresponding genes on a chromosome map. By using Venter´s method an incomplete copy of the gene, called expressed sequence tag (EST), is acquired. ESTs are useful for localizing and orienting the mapping and sequence data reported from many different laboratories and serve as landmarks on the developing physical map of the human genome.

Shotgun method speeds up genome analysis

In 1995, Venter and co-workers succeeded in sequencing an entire organism’s genome, the H. influenzae bacterium. During this work, they introduced a method called “whole genome shotgun sequencing”. The shotgun method involves randomly sequencing tiny cloned sections of the genome, with no foreknowledge of where on a chromosome the section originally came from. The partial sequences obtained are then reassembled to a complete sequence by use of computers. The advantage with this method is that it eliminates the need for time-consuming mapping.

A reference DNA sequence of the human genome

By competing (and cooperating) the governmentally financed human genome project (HGP) and the private biotechnology company Celera has completed a reference DNA sequence of the human genome. Both parties made their information simultaneously available in February 2001, by publishing it in on the Internet and in the scientific journals Nature and Science.
One important conclusion of the survey was that humans only have in the order of 30 000 genes, which is far less than the expected 100 000. On the other hand, the genes turned out to be more versatile than previously known. One single gene may have several different functions, depending on the circumstances.