DNA barcoding, while a powerful tool for species identification, comes with several limitations that can impact its accuracy and applicability.
Here are the primary disadvantages of DNA barcoding:
1. Potential for Inaccurate Results
DNA barcoding faces challenges in delivering precise results under certain conditions:
- Contamination by Other DNA: When a sample contains a large amount of DNA from another species (e.g., environmental DNA, gut contents, or tissue from a different organism), it can lead to misleading or inaccurate identification. The presence of excess foreign DNA can obscure or interfere with the target DNA sequence, making it difficult to obtain a clear barcode for the intended species.
- Degraded DNA Samples: DNA barcoding relies on the amplification of specific DNA regions. If the DNA in a sample is severely degraded (broken down into smaller fragments due to age, poor preservation, or environmental exposure), it may be impossible to amplify the necessary barcode region effectively. This can result in no data or incomplete, unreliable sequences.
2. Inability to Identify Hybrid Species
A significant limitation of DNA barcoding is its ineffectiveness in distinguishing hybrid species:
- Naturally Hybridizing Species: DNA barcoding cannot reliably identify species that naturally hybridize or are the product of hybridization events. This is because hybrids possess a mix of genetic material from their parent species, which can lead to ambiguous or intermediate barcode sequences that do not distinctly match a single known species in a reference database.
3. Challenges with Plant Species
Creating reliable DNA barcodes has proven particularly difficult for the plant kingdom:
- Difficulty in Developing Universal Barcodes: Unlike animals, where the mitochondrial cytochrome c oxidase subunit I (COI) gene serves as a widely accepted barcode, plants lack a single, consistently effective universal DNA barcode region. The development of reliable and discriminatory barcode markers for plants has been challenging due to factors like slower mutation rates in some plant genes and the complex evolutionary history of plant chloroplast DNA, which is often used for barcoding. This often necessitates the use of multiple gene regions, increasing complexity and cost.
Understanding these limitations is crucial for researchers and practitioners to properly apply DNA barcoding technology and interpret its results effectively.
