so it would be lost. allelic drop-in can also occur when there is low-template dna because sometimes the stutter peak can be amplified. the stutter is an artifact of pcr. during the pcr reaction, dna polymerase will come in and add nucleotides off of the primer, but this whole process is very dynamic, meaning that the dna polymerase is constantly binding, popping off and then rebinding. therefore, sometimes dna polymerase will rejoin at the short tandem repeat ahead of it, leading to a short tandem repeat that is 1 repeat less than the template. during pcr, if dna polymerase happens to bind to a locus in stutter and starts to amplify it to make lots of copies, then this stutter product will appear randomly in the electropherogram, leading to allelic drop-in. ministr analysis in instances in which dna samples are degraded, like if there are intense fires or all that remains are bone fragments, standard str testing on those samples can be inadequate. when standard str testing is done on highly degraded samples, the larger str loci often drop out, and only partial dna profiles are obtained. partial dna profiles can be a powerful tool, but the probability of a random match is larger than if a full profile was obtained. one method that has been developed to analyse degraded dna samples is to use ministr technology. in the new approach, primers are specially designed to bind closer to the str region. in normal str testing, the primers bind to longer sequences that contain the str region within the segment. ministr analysis, however, targets only the str location, which results in a dna product that is much smaller. by placing the primers closer to the actual str regions, there is a higher chance that successful amplification of this region will occur. successful amplification of those str regions can now occur, and more complete dna profiles can be obtained. the success that smaller pcr products produce a higher success rate with highly degraded samples was first reported in 1995, when ministr technology was used to identify victims of the waco fire. dna mixtures mixtures are another common issue faced by forensic scientists when they are analyzing unknown or questionable dna samples. a mixture is defined as a dna sample that contains two or more individual contributors. that can often occur when a dna sample is swabbed from an item that is handled by more than one person or when a sample contains both the victim's and the assailant's dna. the presence of more than one individual in a dna sample can make it challenging to detect individual profiles, and interpretation of mixtures should be performed only by highly trained individuals. mixtures that contain two or three individuals can be interpreted with difficulty. mixtures that contain four or more individuals are much too convoluted to get individual profiles. one common scenario in which a mixture is often obtained is in the case of sexual assault. a sample may be collected that contains material from the victim, the victim's consensual sexual partners, and the perpetrator(s). mixtures can generally be sorted into three categories: type a, type b, and type c. type a mixtures have alleles with similar peak-heights all around, so the contributors cannot be distinguished from each other. type b mixtures can be deconvoluted by comparing peak-height ratios to determine which alleles were donated together. type c mixtures cannot be safely interpreted with current technology because the samples were affected by dna degradation or having too small a quantity of dna present. when looking at an electropherogram, it is possible to determine the number of contributors in less complex mixtures based on the number of peaks located in each locus. in comparison to a single source profile, which will only have one or two peaks at each locus, a mixture is when there are three or more peaks at two or more loci. if there are three peaks at only a single locus, then it is possible to have a single contributor who is tri-allelic at that locus. two person mixtures will have between two and four peaks at each locus, and three person mixtures will have between three and six peaks at each locus. mixtures become increasingly difficult to deconvolute as the number of contributors increases. as detection methods in dna profiling advance, forensic scientists are seeing more dna samples that contain mixtures, as even the smallest contributor can now be detected by modern tests. the ease in which forensic scientists have in interpenetrating dna mixtures largely depends on the ratio of dna present from each individual, the genotype combinations, and the total amount of dna amplified. the dna ratio is often the most important aspect to look at in determining whether a mixture can be interpreted. for example, if a dna sample had two contributors, it would be easy to interpret individual profiles if the ratio of dna contributed by one person was much higher than the second person. when a sample has three or more contributors, it becomes extremely difficult to determine individual profiles. fortunately, advancements in probabilistic genotyping may make that sort of determination possible in the future. probabilistic genotyping uses complex computer software to run through thousands of mathematical computations to produce statistical likelihoods of individual genotypes found in a mixture. dna databases an early application of a dna database was the compilation of a mitochondrial dna concordance, prepared by kevin w. p. miller and john l. dawson at the university of cambridge from 1996 to 1999 from data collected as part of miller's phd thesis. there are now several dna databases in existence around the world. some are private, but most of the largest databases are government-controlled. the united states maintains the largest dna database, with the combined dna index system (codis) holding over 13 million records as of may 2018. the united kingdom maintains the national dna database (ndnad), which is of similar size, despite the uk's smaller population. the size of this database, and its rate of growth, are giving concern to civil liberties groups in the uk, where police have wide-ranging powers to take samples and retain them even in the event of acquittal. the conservative–liberal democrat coalition partially addressed these concerns with part 1 of the protection of freedoms act 2012, under which dna samples must be deleted if suspects are acquitted or not charged, except in relation to certain (mostly serious and/or sexual) offenses. public discourse around the introduction of advanced forensic techniques (such as genetic genealogy using public genealogy databases and dna phenotyping approaches) has been limited, disjointed, unfocused, and raises issues of privacy and consent that may warrant the establishment of additional legal protections. the u.s. patriot act of the united states provides a means for the u.s. government to get dna samples from suspected terrorists. dna information from crimes is collected and deposited into the codis database, which is maintained by the fbi. codis enables law enforcement officials to test dna samples from crimes for matches within the database, providing a means of finding specific biological profiles associated with collected dna evidence. when a match is made from a national dna databank to link a crime scene to an offender having provided a dna sample to a database, that link is often referred to as a cold hit. a cold hit is of value in referring the police agency to a specific suspect but is of less evidential value than a dna match made from outside the dna databank. fbi agents cannot legally store dna of a person not convicted of a crime. dna collected from a suspect not later convicted must be disposed of and not entered into the database. in 1998, a man residing in the uk was arrested on accusation of burglary. his dna was taken and tested, and he was later released. nine months later, this man's dna was accidentally and illegally entered in the dna database. new dna is automatically compared to the dna found at cold cases and, in this case, this man was found to be a match to dna found at a rape and assault case one year earlier. the government then prosecuted him for these crimes. during the trial the dna match was requested to be removed from the evidence because it had been illegally entered into the database. the request was carried out. the dna of the perpetrator, collected from victims of rape, can be stored for years until a match is found. in 2014, to address this problem, congress extended a bill that helps states deal with "a backlog" of evidence. considerations in evaluating dna evidence when using rflp, the theoretical risk of a coincidental match is 1 in 100 billion (100,000,000,000) although the practical risk is actually 1 in 1,000 because monozygotic twins are 0.2% of the human population. moreover, the rate of laboratory error is almost certainly higher than that and actual laboratory procedures often do not reflect the theory under which the coincidence probabilities were computed. for example, coincidence probabilities may be calculated based on the probabilities that markers in two samples have bands in precisely the same location, but a laboratory worker may conclude that similar but not precisely-identical band patterns result from identical genetic samples with some imperfection in the agarose gel. however, in that case, the laboratory worker increases the coincidence risk by expanding the criteria for declaring a match. studies conducted in the 2000s quoted relatively-high error rates, which may be cause for concern. in the early days of genetic fingerprinting, the necessary population data to compute a match probability accurately was sometimes unavailable. between 1992 and 1996, arbitrary-low ceilings were controversially put on match probabilities used in rflp analysis, rather than the higher theoretically computed ones. evidence of genetic relationship it is possible to use dna profiling as evidence of genetic relationship although such evidence varies in strength from weak to positive. testing that shows no relationship is absolutely certain. further, while almost all individuals have a single and distinct set of genes, ultra-rare individuals, known as "chimeras", have at least two different sets of genes. there have been two cases of dna profiling that falsely suggested that a mother was unrelated to her children. fake dna evidence the functional analysis of genes and their coding sequences (open reading frames ) typically requires that each orf be expressed, the encoded protein purified, antibodies produced, phenotypes examined, intracellular localization determined, and interactions with other proteins sought. in a study conducted by the life science company nucleix and published in the journal forensic science international, scientists found that an in vitro synthesized sample of dna matching any desired genetic profile can be constructed using standard molecular biology techniques without obtaining any actual tissue from that person. dna evidence in criminal trials evidence part of the law series types of evidence testimony documentary real (physical) digital exculpatory inculpatory demonstrative eyewitness identification genetic (dna) lies relevance burden of proof laying a foundation materiality public policy exclusions spoliation character habit similar fact authentication chain of custody judicial notice best evidence rule self-authenticating document ancient document hague evidence convention witnesses competence privilege direct examination cross-examination redirect impeachment recorded recollection expert witness dead man's statute hearsay and exceptions in english law in united states law confessions business records excited utterance dying declaration party admission ancient document declaration against interest present sense impression res gestae learned treatise implied assertion other common law areas contract tort property wills, trusts and estates criminal law familial dna searching familial dna searching (sometimes referred to as "familial dna" or "familial dna database searching") is the practice of creating new investigative leads in cases where dna evidence found at the scene of a crime (forensic profile) strongly resembles that of an existing dna profile (offender profile) in a state dna database but there is not an exact match. after all other leads have been exhausted, investigators may use specially developed software to compare the forensic profile to all profiles taken from a state's dna database to generate a list of those offenders already in the database who are most likely to be a very close relative of the individual whose dna is in the forensic profile. familial dna database searching was first used in an investigation leading to the conviction