DNA Barcoding: A Molecular Toolkit for Species Identification
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Introduction
🧬DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. It is a long, thin molecule that carries our genetic code and is coiled up tightly inside the nucleus of every cell in our body.
🧬DNA barcoding is a molecular technology that allows the identification of any biological species by amplifying, sequencing, and querying the information from genic and/or intergenic standardized target regions belonging to the extranuclear genomes. It is an approach that involves sequencing short DNA sequences from standardized regions and comparison to a reference database as a molecular diagnostic tool in species identification.
The structure of DNA
🧬DNA, or deoxyribonucleic acid, is a long polymer made from repeating units called nucleotides. The structure of DNA is dynamic along its length, capable of coiling into tight loops and other shapes. In all species, it is composed of two helical chains, bound to each other by hydrogen bonds.
❇️Each strand of a DNA molecule is composed of a long chain of monomer nucleotides. The nucleotides of DNA consist of a deoxyribose sugar molecule to which is attached a phosphate group and one of four nitrogenous bases: two purines (adenine and guanine) and two pyrimidines (cytosine and thymine). The nucleotides are joined together by covalent bonds between the phosphate of one nucleotide and the sugar of the next, forming a phosphate-sugar backbone from which the nitrogenous bases protrude.
✨One strand is held to another by hydrogen bonds between the bases; the sequencing of this bonding is specific—i.e., adenine bonds only with thymine, and cytosine only with guanine.
📌In 1953 James Watson and Francis Crick, aided by the work of biophysicists Rosalind Franklin and Maurice Wilkins, determined that the structure of DNA is a double-helix polymer, a spiral consisting of two DNA strands wound around each other.
Function of DNA
🧬DNA is the information molecule. It stores instructions for making other large molecules, called proteins. These instructions are stored inside each of your cells, distributed among 46 long structures called chromosomes. These chromosomes are made up of thousands of shorter segments of DNA, called genes.
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🧬DNA is well-suited to perform this biological function because of its molecular structure, and because of the development of a series of high-performance enzymes that are fine-tuned to interact with this molecular structure in specific ways.
⭕Apart from being responsible for the inheritance of genetic information in all living beings, DNA also plays a crucial role in the production of proteins.
How much DNA is in your body?
🌱Every human being has about ten trillion cells in their body. Each cell contains DNA packaged into 46 chromosomes in the nucleus. The DNA in your cells is arranged as a coil of coils of coils of coils of coils! This allows the 3 billion base pairs in each cell to fit into a space just 6 microns across.
How far can your DNA stretch?
❇️If all DNA cells are stretched, they can go as far as 744 million miles. That's enough to stretch to the moon and back again almost 1500 times, and reach the Sun and come back four times! If you stretched the DNA in one cell all the way out, it would be about 2m long and all the DNA in all your cells put together would be about twice the diameter of the Solar System.
📢 Isn't it amazing something so small can stretch so far?
What is DNA Barcoding?
🧬DNA barcoding is a powerful taxonomic tool to identify and discover species. With the emergence of new sequencing techniques, such as Next-generation sequencing (NGS), ONT MinION nanopore sequencing, and Pac Bio sequencing, DNA barcoding has become more accurate, fast, and reliable. Rapid species identification by DNA barcodes has been used in a variety of fields, including forensic science, control of the food supply chain, and disease understanding.
🔼The Consortium for Barcode of Life (CBOL) presents various working groups to identify the universal barcode gene, such as COI in metazoans; rbcL, matK, and ITS in plants; ITS in fungi; 16S rRNA gene in bacteria and archaea, and creating a reference DNA barcode library.
The Process of DNA Barcoding
- a) Sample Collection: Biological samples, such as tissue, feathers, scales, or even environmental DNA (eDNA), are collected from the target organism or its surroundings.
- b) DNA Extraction: DNA is extracted from the collected sample using various methods to obtain a pure and concentrated DNA template.
- c) PCR Amplification: The COI gene region is specifically amplified using polymerase chain reaction (PCR) with primers designed for universal applicability across diverse species.
- d) DNA Sequencing: The amplified DNA is then subjected to DNA sequencing to determine the nucleotide sequence of the target gene region.
- e) Data Analysis: The obtained DNA sequence is compared against a reference barcode database, such as the Barcode of Life Data Systems (BOLD), to identify the species based on the closest match or a specified threshold.
Photo - DNA Barcoding | Wikimedia Commons
Advantages of DNA Barcoding
🧬DNA barcoding has several advantages over traditional taxonomic methods. It is faster, more accurate, and more reliable. It can also be used to identify cryptic species and phenotypic plasticity that are difficult to identify using traditional methods.
🥬Constructing a reference library with high species coverage would be a major step toward identifying species by DNA barcodes. This can be achieved in a short period of time by using advanced sequencing and data analysis methods.
⭕ Some more Advantages of DNA Barcoding
- a) Rapid and Accurate Species Identification: DNA barcoding enables quick and reliable identification of species, even for life stages or specimens with limited morphological features.
- b) Discovering Cryptic Species: DNA barcoding has uncovered numerous cryptic species that appear identical morphologically but exhibit distinct genetic differences, shedding light on hidden biodiversity.
- c) Assessing Species Distributions and Invasive Species Monitoring: DNA barcoding aids in tracking and monitoring the distribution of species, including invasive species, by identifying their presence in different regions.
- d) Conservation and Forensic Applications: DNA barcoding supports conservation efforts by assisting in the identification of endangered or protected species, monitoring wildlife trade, and detecting species fraud.
- e) Evolutionary and Ecological Studies: By providing a standardized genetic marker, DNA barcoding helps unravel evolutionary relationships, population genetics, and ecological interactions among species.
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Challenges and Future Directions
- a) Reference Library Expansion: The success of DNA barcoding relies on the availability of comprehensive reference libraries encompassing a wide range of species, prompting the need for ongoing efforts to increase their coverage.
- b) Barcode Gap and Hybridization: Some challenges arise when distinguishing closely related species or hybrid individuals due to insufficient genetic divergence or introgression.
- c) Technical Advances: Technological advancements, such as portable DNA sequencers and miniaturized laboratory equipment, have the potential to make DNA barcoding more accessible and applicable in the field.
- d) Integrating Other Genetic Markers: Expanding the use of additional gene regions or genomic approaches alongside COI can enhance species identification accuracy and provide additional insights into evolutionary relationships.
Conclusion
📌DNA barcoding has revolutionized the field of species identification, providing a powerful molecular toolkit that complements traditional taxonomic methods. This technology offers rapid, accurate, and objective species identification, helping scientists, conservationists, and policymakers better understand and conserve the vast biodiversity of our planet. With ongoing advancements and collaborations, DNA barcoding holds the promise of transforming our knowledge of species diversity, ecological interactions, and evolutionary processes.
What do you think? Have you ever thought about how much DNA is in your body and how far it can stretch? Have you ever heard of DNA barcoding before?
📚 Sources:
1) Your DNA can stretch to the moon - DNA India
2)How long is your DNA? | BBC Science Focus Magazine.
3) Length of uncoiled human DNA - Skeptics Stack Exchange.
4) DNA - Wikipedia.
5) DNA | Definition, Discovery, Function, Bases, Facts, & Structure. | Britannica
6) Structure of DNA - Higher Biology Revision - BBC
7) DNA - Definition, Function, Structure and Discovery - Biology Dictionary.
8) DNA Barcoding as a Molecular Tool to Track Down Mislabeling and ... - MDPI
9) DNA Barcoding: A Potential Tool for Invasive Species Identification
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