DNA from all organisms is made up from the same chemical and physical components. Each sequence has a particular arrangement and each order spells out exact instructions to create a specific organism with its own unique characteristics and traits.
DNA sequencing is the determination of the exact sequence of the 3 billion chemical building blocks (called nucleotides abbreviated A, T, C, and G) that make up the DNA of a human being’s 24 different chromosomes. This is the greatest technical challenge in the Human Genome Project. Achieving this goal has helped reveal the estimated 30,000 human genes within our DNA. It has also helped us figure out what each of them does and how we can control them. These DNA maps are being used by scientists to explore human biology and other complex phenomena.
The process of DNA sequencing is very elaborate. Methods such as separating DNA fragments by gel electrophoresis (which is, incidentally, extremely laborious and expensive) have been used. These use tiny tubes to run standard electrophoretic separations. These work much faster because the tubes scatter heat well and allow much higher electrical fields to complete sequencing in a shorter amount of time.
The sequencing is done by a very complex process. Chromosomes range in size from 50 million to 250 million bases and must be broken down into much shorter pieces. Each short piece is used as a template to form a set of fragments that vary in length from each other by a single base that will be later identified. The fragments in each set are then separated by gel electrophoresis. New dyes allow separation of all four fragments in a single lane on the gel. The final base at the end of each fragment is then identified. It recreates the original sequence of As, Ts, Cs, and Gs for each short piece produced in the first step. The resulting pieces are analyzed. After each base is “read,” computers assemble the short sequences into long stretches that are analyzed for errors, gene-coding regions, and to determine important characteristics.
Past genomes have been already discovered through this sequencing. Small genomes of several viruses and bacteria and much larger genomes of higher organisms have already been completely sequenced. They are called bakers or brewers’ yeast, the roundworm, and the fruit fly. Scientists have also determined the sequence of their first plant, the weed called Arabidopsis thaliana. Daily, more and more genomes are being completed.
The advantages of DNA sequencing are endless. Deriving meaningful knowledge from the sequences will take decades of research and require expertise and creativity in biologists, chemists, engineers, and computer scientist. Some of the following are advances that will come of these findings:
- Numbering genes, their exact locations and their functions
- Regulating genes
- Organizing chromosome structure
- Organizing gene types, amounts, distribution, content, and functions
- Predicting gene functions
- Conservation among organisms
- Disease control
- Genetics advances
This DNA sequencing is a difficult and confusing process but the results and the benefits are countless. When the world of science finishes DNA sequencing for all plants and animals, the possibilities are endless.
By Jessica Maughan