The discovery of DNA and its function has revolutionized the way we understand and interact with the biological world. The key technology built on this discovery is DNA sequencing, which enables us to ‘read’ DNA sequences. By decoding the genetic sequence, we gain insight into what makes each organism and individual unique, and apply the knowledge to a wide range of biological fields, from evolutionary biology to human health. This article will explain what DNA sequencing is, how it works, and how it is utilized in society.
What is DNA sequencing?
To understand DNA sequencing, one must first understand DNA. Every organism, from bacteria to humans, carries DNA in its cells. DNA is made up of four building blocks called nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). The order of these nucleotides instructs cells on how to build and maintain the organism.
DNA sequencing is simply the process of determining the exact sequence of nucleotides in a DNA molecule. Sequencing is done using specialized machines, which take DNA as input and generate text files that show the order of nucleotide sequences.
How Does DNA Sequencing Work?
DNA sequencing reads the order of nucleotides in a strand of DNA using specialized machines. Due to the chemical properties of DNA and the characteristics of different sequencing machines, DNA needs to be prepared in specific ways to be sequenced. The following are the key steps for the most common DNA sequencing approach.
DNA is collected from various sources, such as blood, tissue, hair, bones, or even dead skin. Environmental sources like soil, water, or air can contain DNA left behind by organisms, which can be sequenced.
Once samples are collected, DNA is separated from everything else in the samples, such as dirt, proteins and fats. A combination of physical and chemical procedures is used to separate the DNA.
The raw DNA cannot be directly sequenced by the machine. Therefore, DNA is processed by cutting it into smaller pieces. These fragments are then tagged so the machine can identify and read them, and the DNA content can be amplified if the volume is insufficient. This process is called ‘library preparation’ because the tagged DNA fragments are organized like books in a library, making them readable by the DNA sequencer.
The processed DNA, now consisting of many fragmented pieces, is then loaded into the machine to have its sequences determined. The machine can read DNA fragments simultaneously and outputs files that contain the sequences of all the fragmented reads.
While the sequencing process generates data, the raw output of nucleotide sequences require further processing to be interpreted. Specialized software assembles the DNA fragments in the correct order to reconstruct the full DNA sequence. Depending on the application, the data is then analyzed differently.
Why is DNA Sequencing Important?
The applications of DNA sequencing are vast, and each application can be exciting and impactful. Below are some key areas where sequencing technology plays a crucial role.
- Evolutionary Biology:
The evolutionary history of species can be inferred by comparing DNA data across organisms. The similarities and differences across DNA signatures provide insights into how species relate and how species diverged. These insights combined with the knowledge of the geologic and the climatic past provide us with stories of population size dynamics and the movement of the present day and extinct species. - Conservation and Ecology:
DNA data can inform conservation decisions through insights on population health and species range. A healthy population usually has individuals that differ from each other in various ways, and DNA sequencing uncovers the genetic diversity of a population. Sequencing can also detect rarely observed species and identify cryptic species that are hard to distinguish physically. Understanding species range and the presence/absence of rare species helps inform land-use decisions. - Agriculture:
Sequencing technologies allow for the identification and selection of desirable genetic traits in crops and livestock. Desired traits such as crop yield and disease resistance are most often genetic, and sequencing technology can discover the reasons behind these traits, which accelerates breeding programs and helps develop more sustainable agricultural practices. - Healthcare and Medicine:
DNA sequencing is crucial in diagnosing a wide range of conditions, from inherited diseases to cancer, and in guiding personalized treatments. By identifying disease-causing mutations, it enables early interventions and supports the development of gene-based therapies. - Epidemiology:
In epidemiology, DNA sequencing is crucial for tracking the spread and mutation of pathogens such as viruses and bacteria. By analyzing genetic sequences of infectious agents like COVID-19, public health officials can monitor outbreaks, understand transmission patterns, and develop targeted responses to control disease spread. - Forensics:
DNA sequencing is a powerful tool in forensic science, used to identify individuals based on genetic material left at crime scenes. As each individual has a unique genetic signature, sequencing enables precise identification for criminal investigations, paternity testing, and even identifying victims in mass casualty events or cold cases.
Conclusion
To conclude, DNA sequencing is the process of determining the exact sequence of nucleotides in a DNA molecule. Whether it’s understanding the origins of species, conserving endangered populations, enhancing agricultural productivity, improving human health, tracking disease outbreaks, or solving crimes, DNA sequencing plays a major role. As technology advances and costs decrease, the applications of DNA sequencing will continue to grow, offering even greater insights and innovations.
