Genome Sequencing & Its Methods
Genome sequencing is the process of determining the nucleic acid sequence and precise order of nucleotides in the genome. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. It is a simple process in which the whole genome is broken into pieces, sequencing the pieces and then reassembling these pieces in a proper order to reach the sequence of the whole genome.
DNA sequencing methods were first developed more than 20 years ago with the publication of two approaches to sequencing methodology that became known as Sanger sequencing and Maxim-Gilbert sequencing, which involved chemical degradation of end-radio-labeled DNA fragments. Both methods relied on four-lane, high resolution polyacrylamide gel electrophoresis to separate the labeled fragment and allow the base sequence to be read in a staggered ladder-like fashion.
The phi X 174 (or ΦX174) bacteriophage is a single-stranded DNA virus that infects Escherichia coli, and the first DNA-based genome to be sequenced. This work was completed by Fred Sanger and his team in 1977. Completion of the sequence marked a significant turning point in DNA sequencing because it was achieved with no prior genetic profile knowledge of the virus.
Advantages of genomic sequencing
In principle, full genome sequencing can provide the raw nucleotide sequence of an individual organism’s DNA. However, further analysis must be performed to provide the biological or medical meaning of this sequence, such as how this knowledge can be used to help prevent disease.
- helping scientists find genes much more easily and quickly
- deciphering code of life
- typing microorganisms
- detecting of mutations
- identifying Human haplotypes
- designating polymorphisms
- helps in the knowledge how the genome as a whole works, how genes work together to direct the growth, development and maintenance of an entire organism
- finding of the regulatory regions
- detect a wide range of variants
- size of genomes for comparison
- used in medical diagnostics and forensics
- identifying regions of DNA associated with particular features, including specific diseases or increased susceptibility to specific diseases
- understanding gene expression and how different genes interact
- identification of substances, individuals and species
- other genetic technologies such as gene therapy, genealogy research, plant and animal breeding and genetic modification.
It requires breaking the DNA of the genome into many smaller pieces, sequencing the pieces, and assembling the sequences into a single long “consensus.” However, new methods that have been developed over the past two decades, genome sequencing, is now much faster and less expensive than it was during the Human. Modern sequencing equipment uses the principles of the Sanger technique.
Factors that determine sequencing methods are;
- Genome size
- Chromosomal structure
- Repeat content and character
- Desired end product
Genome sequencing methods
Various methods of DNA sequencing are enlisted here;
- Maxam and Gilbert method
- Chain termination method
- Semiautomated method
- Automated method
- The whole-genome shotgun sequencing method
- Clone by the clone sequencing method
- Next-generation sequencing method