Unless you are an experienced geneticist, you are likely to have some questions about the intricacies of DNA sequencing. In particular, the complex processes of PCR amplification and next generation sequencing.
Read on for answers to some of the most frequently asked questions about DNA and the next generation sequencing techniques and modalities that are driving the field of genetics into the future.
What is DNA sequencing?
As defined by the National Human Genome Research Institute of the National Institutes of Health, DNA sequencing is the process of determining the order of the four basic chemical building blocks (or “bases”) of the DNA molecule. First modeled by the legendary research team of James Watson, Francis Crick, and J. Rosalind Franklin in the early 1950s, the double helix structure of DNA contains the bases cytosine, thymine, adenine, and guanine. Molecular geneticists have employed a range of evolving methods to identify the ordered sequence of these bonding bases.
Why do scientists sequence DNA?
Determining the sequential order of base bonds in a DNA segment is essential if scientists are to garner any firm understanding of the genetic information that particular segment carries. In the words of the National Human Genome Research Institute, “scientists can use sequence information to determine which stretches of DNA contain genes and which stretches carry regulatory instructions, turning genes on or off. In addition, and importantly, sequence data can highlight changes in a gene that may cause disease.”
How do scientists sequence DNA?
Since the days of Watson, Crick, and Franklin, molecular geneticists have developed a variety of methods for DNA sequencing. Developed by Frederick Sanger in 1977, Sanger sequencing was the prevailing DNA sequencing method for several decades. In fact, the Human Genome Project used this method to map the whole human genome in the 1990s and early 2000s. However, due to the relatively labor-intensive and time-consuming nature of Sanger sequencing, it took Human Genome Project researchers a full 13 years to complete this project. Thanks to the advent of next generation sequencing methods, scientists of today can sequence an entire human genome in between 24 and 48 hours.
Why is PCR used in DNA sequencing?
Typically a required step in Sanger sequencing, PCR ushered in the modern age of automated and next generation sequencing that molecular geneticists enjoy today. Short for polymerase chain reaction, PCR was invented in 1985 by Kary B. Mullis. The PCR technique enables scientists to copy and amplify any targeted DNA sequence. It is particularly essential when dealing with DNA samples that are extremely small or scarce. PCR’s ability to make nearly infinite copies of a DNA segment has transformed research, including the way genetic defects are diagnosed and how AIDS in human cells is detected.
What is next generation DNA sequencing?
A blanket term that covers a number of techniques and modalities, next generation sequencing (NGS) is generally defined by automation and efficiency. NGS methods are exponentially faster and less expensive than the Sanger technique and other DNA sequencing methods that came before them. Wise researchers will apply the right sequencing method for the project at hand, considering factors that range from desired application to budgetary restrictions. According to the innovative technology company Illumina, “NGS technology has fundamentally changed the kinds of questions scientists can ask and answer.” In addition to dramatically reducing the time it takes to sequence entire genomes, NGS has given scientists the ability to efficiently complete deep sequencing in target regions. It has also helped researchers identify novel pathogens and study the human microbiome in its entirety.