Biotechnology Terms Starting With D
Biotechnology Glossary: D
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DNA Fingerprinting
/ dee-en-ay FING-ger-prin-ting / · Deoxyribonucleic Acid; finger + print
DNA fingerprinting is a technique that identifies individuals based on unique patterns of variable DNA sequences, used in forensic science, paternity testing, and population genetics.
Developed by Alec Jeffreys in 1984, the original method detected restriction fragment length polymorphisms using Southern blotting. Modern forensic DNA profiling uses short tandem repeat analysis, which amplifies 13 to 20 highly variable genomic loci by PCR and resolves them by capillary electrophoresis. The probability of two unrelated individuals sharing the same STR profile across the FBI’s CODIS 20-locus panel is less than one in a quadrillion.
STR profiling requires as little as 100 to 200 picograms of DNA, making it applicable to trace biological evidence.
Jeffreys first applied DNA fingerprinting to a criminal case in 1986, when it exonerated an innocent suspect and identified Colin Pitchfork as the perpetrator of two murders in Leicestershire, England, after police screened DNA from more than 4,000 local men.
DNA fingerprinting reveals an individual's traits, ancestry, or disease risks. Forensic STR profiles examine only a small set of non-coding markers chosen for variability between individuals, not for any information they encode about biology or health.
Wildlife forensic scientists use DNA fingerprinting to identify the species and individual origin of illegally traded animal products. In one documented case, STR profiling of elephant (Loxodonta africana) ivory traced shipments to specific poaching sites in central Africa, linking traffickers to particular elephant populations.
DNA Microarray
/ dee-en-ay MY-kroh-uh-ray / · Deoxyribonucleic Acid; Greek mikros, small; Old French areer, to array
DNA microarray is a solid surface onto which thousands of specific DNA sequences are affixed in defined positions, enabling simultaneous measurement of the expression level of thousands of genes in a single experiment.
Fluorescently labeled cDNA from a sample hybridizes to complementary probes on the array, and the intensity of fluorescence at each spot reflects the abundance of the corresponding mRNA. Microarrays revolutionized gene expression profiling by enabling genome-wide transcriptomic studies in the early 2000s before RNA sequencing largely supplanted them for many applications. A single Affymetrix GeneChip array can carry probes for more than 20,000 human genes on a surface smaller than a postage stamp.
Microarrays remain widely used for genotyping single nucleotide polymorphisms in genome-wide association studies linking genetic variants to disease.
Microarrays were central to the landmark 2000 study by Perou and colleagues that classified breast cancer into molecularly distinct subtypes, including luminal and HER2-enriched categories, based on gene expression patterns across 8,102 genes. That classification still informs treatment decisions today.
Building Blocks of Nucleic Acids →Microarrays sequence DNA base by base. They detect whether known sequences are present or measure how strongly genes are expressed by capturing labeled molecules at spots with complementary sequences, without reading any new sequence information.
Researchers studying Arabidopsis thaliana used microarrays to measure changes in expression across roughly 22,000 genes when plants were exposed to drought stress. Genes encoding dehydrin proteins showed more than eightfold increases in transcript abundance within 24 hours of water withdrawal.
DNA Sequencing
/ dee-en-ay SEE-kwen-sing / · Deoxyribonucleic Acid; Latin sequi, to follow
DNA sequencing is the process of determining the precise order of nucleotide bases along a DNA strand or entire genome.
Frederick Sanger developed chain-termination sequencing in 1977, which remained the gold standard for over two decades and underpinned the Human Genome Project completed in 2003. Next-generation sequencing platforms now sequence billions of base pairs simultaneously through massively parallel approaches including reversible terminator chemistry and semiconductor ion detection. A modern short-read sequencer can generate more than one terabase of sequence data in a single 48-hour run, at a cost that has dropped below $1,000 per human genome.
The resulting data enables identification of mutations, structural variants, and microbial community compositions in samples ranging from patient biopsies to ocean water.
Oxford Nanopore sequencing devices, some no larger than a USB drive, were deployed in West Africa during the 2014 to 2016 Ebola outbreak to sequence viral genomes in the field within hours of sample collection, allowing researchers to track transmission chains in near real time without shipping samples to distant laboratories.
Sequencing a genome instantly explains everything about an organism. A raw sequence must still be assembled from millions of short fragments, annotated to identify genes, and compared against reference databases before any biological meaning can be extracted.
Clinical microbiologists sequence the genomes of Mycobacterium tuberculosis isolates from patients with drug-resistant tuberculosis to identify which specific mutations in genes such as rpoB and katG confer resistance to rifampicin and isoniazid. A complete genome sequence of about 4.4 megabases can be obtained in under 24 hours using next-generation platforms, guiding treatment selection before culture-based drug sensitivity results are available.