dna profiling dna profiling dna profiling (also called dna fingerprinting and genetic fingerprinting) is the process of determining an individual's deoxyribonucleic acid (dna) characteristics. dna analysis intended to identify a species, rather than an individual, is called dna barcoding. for dna testing for inherited diseases, see genetic testing. part of a series onforensic science physiological anthropology biology bloodstain pattern analysis dentistry dna phenotyping dna profiling entomology epidemiology limnology medicine palynology pathology podiatry toxicology social psychiatry psychology psychotherapy social work criminalistics accounting body identification chemistry colorimetry election forensics facial reconstruction fingerprint analysis firearm examination footwear evidence forensic arts profiling gloveprint analysis palmprint analysis questioned document examination vein matching forensic geophysics forensic geology digital forensics computer exams data analysis database study malware analysis mobile devices network analysis photography video analysis audio analysis related disciplines electrical engineering engineering fire investigation fire accelerant detection fractography linguistics materials engineering polymer engineering statistics traffic collision reconstruction related articles crime scene csi effect perry mason syndrome pollen calendar skid mark trace evidence use of dna inforensic entomology outline category dna profiling is a forensic technique in criminal investigations, comparing criminal suspects' profiles to dna evidence so as to assess the likelihood of their involvement in the crime. it is also used in paternity testing, to establish immigration eligibility, and in genealogical and medical research. dna profiling has also been used in the study of animal and plant populations in the fields of zoology, botany, and agriculture. background sir alec jeffreys, pioneer of dna profiling. his discovery led to the conviction of colin pitchfork in 1988. starting in the 1980s, scientific advances allowed the use of dna as a material for the identification of an individual. the first patent covering the direct use of dna variation for forensics (us5593832a) was filed by jeffrey glassberg in 1983, based upon work he had done while at rockefeller university in the united states in 1981. british geneticist sir alec jeffreys independently developed a process for dna profiling in 1985 while working in the department of genetics at the university of leicester. jefferys' discovered that a dna examiner could establish patterns in unknown dna. these patterns were a part of inherited traits that could be used to advance the field of relationship analysis. these discoveries lead to the first use of dna profiling in a criminal case. the process, developed by jeffreys in conjunction with peter gill and dave werrett of the forensic science service (fss), was first used forensically in the solving of the murder of two teenagers who had been raped and murdered in narborough, leicestershire in 1983 and 1986. in the murder inquiry, led by detective david baker, the dna contained within blood samples obtained voluntarily from around 5,000 local men who willingly assisted leicestershire constabulary with the investigation, resulted in the exoneration of richard buckland, an initial suspect who had confessed to one of the crimes, and the subsequent conviction of colin pitchfork on january 2, 1988. pitchfork, a local bakery employee, had coerced his coworker ian kelly to stand in for him when providing a blood sample—kelly then used a forged passport to impersonate pitchfork. another coworker reported the deception to the police. pitchfork was arrested, and his blood was sent to jeffrey's lab for processing and profile development. pitchfork's profile matched that of dna left by the murderer which confirmed pitchfork's presence at both crime scenes; he pleaded guilty to both murders. variations of vntr allele lengths in 6 individuals. although 99.9% of human dna sequences are the same in every person, enough of the dna is different that it is possible to distinguish one individual from another, unless they are monozygotic (identical) twins. dna profiling uses repetitive sequences that are highly variable, called variable number tandem repeats (vntrs), in particular short tandem repeats (strs), also known as microsatellites, and minisatellites. vntr loci are similar between closely related individuals, but are so variable that unrelated individuals are unlikely to have the same vntrs. before vntrs and strs, people like jefferys used a process called restriction fragment length polymorphism (rflp). this process regularly used large portions of dna to analyze the differences between two dna samples. rflp was among the first technologies used in dna profiling and analysis. however, as technology has evolved, new technologies, like str, emerged and took the place of older technology like rflp. the admissibility of dna evidence in courts was disputed in the united states in the 1980s and 1990s, but has since become more universally accepted due to improved techniques. profiling processes dna extraction when a sample such as blood or saliva is obtained, the dna is only a small part of what is present in the sample. before the dna can be analyzed, it must be extracted from the cells and purified. there are many ways this can be accomplished, but all methods follow the same basic procedure. the cell and nuclear membranes need to be broken up to allow the dna to be free in solution. once the dna is free, it can be separated from all other cellular components. after the dna has been separated in solution, the remaining cellular debris can then be removed from the solution and discarded, leaving only dna. the most common methods of dna extraction include organic extraction (also called phenol chloroform extraction), chelex extraction, and solid phase extraction. differential extraction is a modified version of extraction in which dna from two different types of cells can be separated from each other before being purified from the solution. each method of extraction works well in the laboratory, but analysts typically select their preferred method based on factors such as the cost, the time involved, the quantity of dna yielded, and the quality of dna yielded. rflp analysis restriction fragment length polymorphismrflp stands for restriction fragment length polymorphism and, in terms of dna analysis, describes a dna testing method which utilizes restriction enzymes to "cut" the dna at short and specific sequences throughout the sample. to start off processing in the laboratory, the sample has to first go through an extraction protocol, which may vary depending on the sample type and/or laboratory sops (standard operating procedures). once the dna has been "extracted" from the cells within the sample and separated away from extraneous cellular materials and any nucleases that would degrade the dna, the sample can then be introduced to the desired restriction enzymes to be cut up into discernable fragments. following the enzyme digestion, a southern blot is performed. southern blots are a size-based separation method that are performed on a gel with either radioactive or chemiluminescent probes. rflp could be conducted with single-locus or multi-locus probes (probes which target either one location on the dna or multiple locations on the dna). incorporating the multi-locus probes allowed for higher discrimination power for the analysis, however completion of this process could take several days to a week for one sample due to the extreme amount of time required by each step required for visualization of the probes. polymerase chain reaction (pcr) analysis main article: polymerase chain reaction str analysis short tandem repeat (str) analysis on a simplified model: first, a dna sample undergoes polymerase chain reaction with primers targeting certain strs (which vary in lengths between individuals and their alleles). the resultant fragments are separated by size (such as electrophoresis). the system of dna profiling used today is based on polymerase chain reaction (pcr) and uses simple sequences. from country to country, different str-based dna-profiling systems are in use. in north america, systems that amplify the codis 20 core loci are almost universal, whereas in the united kingdom the dna-17 loci system is in use, and australia uses 18 core markers. the true power of str analysis is in its statistical power of discrimination. because the 20 loci that are currently used for discrimination in codis are independently assorted (having a certain number of repeats at one locus does not change the likelihood of having any number of repeats at any other locus), the product rule for probabilities can be applied. this means that, if someone has the dna type of abc, where the three loci were independent, then the probability of that individual having that dna type is the probability of having type a times the probability of having type b times the probability of having type c. this has resulted in the ability to generate match probabilities of 1 in a quintillion (1x1018) or more. however, dna database searches showed much more frequent than expected false dna profile matches. y-chromosome analysis due to the paternal inheritance, y-haplotypes provide information about the genetic ancestry of the male population. to investigate this population history, and to provide estimates for haplotype frequencies in criminal casework, the "y haplotype reference database (yhrd)" has been created in 2000 as an online resource. it currently comprises more than 300,000 minimal (8 locus) haplotypes from world-wide populations. mitochondrial analysis mtdna can be obtained from such material as hair shafts and old bones/teeth. control mechanism based on interaction point with data. this can be determined by tooled placement in sample. issues with forensic dna samples when people think of dna analysis, they often think about television shows like ncis or csi, which portray dna samples coming into a lab and being instantly analyzed, followed by the pulling up of a picture of the suspect within minutes⁠. however, the reality is quite different, and perfect dna samples are often not collected from the scene of a crime. homicide victims are frequently left exposed to harsh conditions before they are found, and objects that are used to commit crimes have often been handled by more than one person. the two most prevalent issues that forensic scientists encounter when analyzing dna samples are degraded samples and dna mixtures. degraded dna before modern pcr methods existed, it was almost impossible to analyze degraded dna samples. methods like restriction fragment length polymorphism or rflp restriction fragment length polymorphism, which was the first technique used for dna analysis in forensic science, required high molecular weight dna in the sample in order to get reliable data. high molecular weight dna, however, is lacking in degraded samples, as the dna is too fragmented to carry out rflp accurately. it was only when pcr techniques were invented that analysis of degraded dna samples were able to be carried out polymerase chain reaction. multiplex pcr in particular made it possible to isolate and to amplify the small fragments of dna that are still left in degraded samples. when multiplex pcr methods are compared to the older methods like rflp, a vast difference can be seen. multiplex pcr can theoretically amplify less than 1 ng of dna, but rflp had to have a least 100 ng of dna in order to carry out an analysis. low-template dna low-template dna can happen when there is less than 0.1 ng() of dna in a sample. this can lead to more stochastic effects (random events) such as allelic dropout or allelic drop-in which can alter the interpretation of a dna profile. these stochastic effects can lead to the unequal amplification of the 2 alleles that come from a heterozygous individual. it is especially important to take low-template dna into account when dealing with a mixture dna sample. this is because for one (or more) of the contributors in the mixture, they are more likely to have less than the optimal amount of dna for the pcr reaction to work properly. therefore, stochastic thresholds are developed for dna profile interpretation. the stochastic threshold is the minimum peak height (rfu value), seen in an electropherogram where dropout occurs. if the peak height value is above this threshold, then it is reasonable to assume that allelic dropout has not occurred. for example, if only 1 peak is seen for a particular locus in the electropherogram but its peak height is above the stochastic threshold, then we can reasonably assume that this individual is homozygous and is not missing its heterozygous partner allele that otherwise would have dropped out due to having low-template dna. allelic dropout can occur when you have low-template dna because there is such little dna to start with that at this locus the contributor to the dna sample (or mixture) is a true heterozygote but the other allele is not amplified and