Talk:DNA profiling/Archive 1

Fetal DNA sampling
Is anyone able to contribute information regarding the methods of sampling fetal DNA, whether invasive or non-invasively? I wasn't able to find anything particularly definitive after an hour of online searching.

It would also be useful to add information about the legality of such procedures (including whether they can be the subject of a warrant) and any risks to the fetus that may be involved.


 * Fetal DNA can be extracted from maternal blood after the 12th week of pregnancy (non-invasive), before week 12 an invasive proceedure like Chorionic villus sampling (CVS) and/or Amniocentesis has to be used. I can't comment on the application of law to force either type of proceedure. --nixie 05:08, 11 July 2005 (UTC)

What is Dr. Schneeberger's first name and where in Canada did the 1992 case of fake DNA evidence take place? Please provide a source. Thank you. Dphen 19:56, 10 February 2006 (UTC)

DNA Databanks
With the recent additions by 88.106.31.222, it seems like this article has started to cover more than the scope of just genetic typing. Most of the information about the FSS's databank could be moved to another article just about DNA databanks. Sekiyu 18:25, 26 April 2006 (UTC)

First case
This website lists Tommie Lee Andrews' conviction as 6 Nov 1987 (a quick google search seems to confirm it). This is the year before Colin Pitchfork's conviction is listed by BBC. Can anyone find some source to unmix this? Ted 06:03, 28 April 2006 (UTC)


 * Good question! According to the Gene Technology page you linked, the line "Andrews became the first person in the United States to be convicted of a crime based on DNA evidence" is key.  The Pitchfork case was in the UK, and he while was indeed sentenced in 1988, the investigation itself occurred in early 1987 (he was arrested on Sep 19, 1987 and plead guilty to the rapes and murders). An interesting side note is that the first time that genetic fingerprinting was used for law enforcement, it was actually in the exoneration of an innocent man: George Howard in 1986.  Sekiyu 20:30, 28 April 2006 (UTC)


 * If he plead guilty, then he was not the first conviction due to DNA fingerprinting. Maybe a better wording would be "first criminal caught using DNA fingerprinting."  The Date would then be 1987 (when he was arrested), which would match with the conviction of Andrews.  It might be useful if someone with a law background could verify the "exoneration" (which has a more strict legal definition than popular defintion).  I have made a few changes to that section to clean up the language a little bit. Ted 00:22, 1 May 2006 (UTC)

Hey what about the first person to exonerated from death row. His name is Bloodsworth, Kurt (i think). You can find him on the innocence project's website and someone's wrote a book about him??

DNA mass surveillance
Is there an article giving examples for DNA mass screening ? -- Simplicius 15:05, 28 July 2006 (UTC)

The Southside Strangler case
According to, a Timothy Spencer was the murderer of four females in the famous "southside strangler" case in Virginia. He is known to be the first person jailed and put to death in the United States due to a DNA analysis match in his semen on the four female victims he raped and asphyxiated (or other way around). The case was also mentioned several times in the Forensic Files series, where they also claim that it was the first time ever in the United States where someone was arrested due to circumstantial DNA evidence found in his semen to match on his raped victims. I think that should that be mentioned in the article since that case was also in 1987. Comments anyone? (Me | The Article) 08:01, 13 January 2007 (UTC)

Independent assortment
Is there any research that substantiates the assertion that the loci in the genes are Independently Assorted? Though this is a nice assumption in court, if it is not true then STR testing would be substantially less powerful then claimed to be. I would refer to Keith Devlin's columns in MAA Online for the months of September and October for further reading on why it is important to first establish the assortment independence as fact before using the power rule to establish its statistical accuracy. RSimione 20:57, 29 December 2006 (UTC)


 * Absolutely. Check out and .  JFS is one of the foremost peer-reviewed forensic sciences journals in publication. Sekiyu 16:45, 9 February 2007 (UTC)


 * I read Keith Devlin's article; I found it ironic that he would present some specious arguments himself. His argument sounds strong to a naive reader, but his October article hinges on the Birthday_Paradox.  If you plug his numbers into the formulas that are listed in that article, you will find that in a database of 65,493 entries, you will expect to have a 50% chance of a match with only 301 people.  If you understand the probabilities involved, I think that you will be disappointed by Devlin as well. Sekiyu 17:44, 9 February 2007 (UTC)

Partial Matches (and UK Statistics)
There should be a section (or an article) on partial DNA matches, their usefulness to law enforcement, and the controversies going on now. Also, the FBI's new interstate policies should be noted. Should this be a section or its own article?

Separately; is that "7 million in the UK database" stat correct? I heard an interview with Denver's DA Mitch Morrisey in which he cited the number at just over 3 million. Anyone have a source for this?

-

The US combined national database has about 5 million. The UK database is over 4 million. CharlesBrenner 27 Jan 2007 (UTC)

As of May 2007, the FBI's NDIS webpage states that there are 4,582,516 Total Convicted Offender profiles in the system. . From the minutes of the House of Commons, "Joan Ryan: As of 10 June 2007, there were an estimated 3,976,090 individuals on the National DNA Database (NDNAD)." Furthermore, they estimate that 13.7% of their profiles are duplicates This handily makes the US's NDIS the largest DNA databank in the world. Sekiyu 04:55, 16 August 2007 (UTC)

Also used for plants?
The lead says this technique is used for "individuals," but I believe it is also used to identify the genes of plants. Thus, the lead should be revised. Badagnani (talk) 22:17, 12 December 2007 (UTC)

Extracting DNA from fingerprints
When it comes to DNA left at crime scenes, is it routine to extract copies of DNA directly from the fats and oils of fingerprints, especially for the purpose of comparing them to blood samples found there, to determine how many individuals may have been at the scene of a crime?


 * The fingerprints have to be bloody in order to extract DNA from them. The fats, oils, and salts associated with fingerprints usually lack DNA, a protein.

DNA is not a protein. This is an error I have come across repeatedly on wikipedia discussion pages. DNA is a nucleic acid, which is entirely different from a protein.

If the fingerprints themselves are usable prints (not smudges, for example), they would themselves be used to identify persons from the scene. DNA may get all the glamour nowadays, but latent prints are still very widely used for forensic purposes. In general, if it is thought that a suspect touched something at a crime scene, the item would be processed by latent print examiners.

That said, while the salts, lipids and proteins in latent prints are not generally considered a useful source of DNA, what can be done in some cases is to analyze what is known as "touch DNA," in which an examiner attempts to extract DNA from skin cells left behind when someone touched something, such as the rim of a hat worn, or a steering wheel. This is not "routine," however.

Analysis of touch DNA would be done for the same purpose any other DNA samples--to identify persons present at the scene. To say "especially for the purpose of comparing them to blood samples found there, to determine how many individuals may have been at the scene of a crime" is rather too specific to confirm; in fact it sounds like an episode of CSI. Additionally, if there is plentiful (miniscule amounts are required now) blood (or other common sources such as semen or saliva) available, touch DNA would normally be considered unnecessary.165.176.123.2 (talk) 19:48, 28 February 2008 (UTC)

2003
I don't understand how a 1 in 5 million chance translates into 30 people who would match the profile from a population of 60 million people. Wouldn't that be 12 people (and not 12 other people, 12 people in total)?

Marisano

Agreed. I changed 30 to 12.

Zashaw 02:06, 18 Aug 2003 (UTC)

-

This page seems redundant with DNA testing -- the articles should probably be merged, or, if there's a distinction between the articles, it should be made explicit.

Zashaw 04:24, 18 Oct 2003 (UTC)

So what are the advantages of this system

- The second paragraph mentions PCR, the section on the DNA fingerprinting process doesn't. Which one is correct? Furthermore, what kinds of restriction enzymes/PCR primers are being used? AxelBoldt 16:21, 29 Jul 2004 (UTC)

- The article initially states "...STR profiling...is distinct from DNA fingerprinting...", but later categorizes STR analysis as a type of DNA fingerprinting. Is something missing, or is STR profiling distinct from STR analysis? Ian Glenn 21:34, 3 April 2007 (UTC)

No, they are the same thing. It is a kind of DNA analysis using PCR, which uses primers. RFLP, distinct from PCR, uses restriction enzymes. RFLP is little used now.165.176.123.2 (talk) 19:54, 28 February 2008 (UTC)

Copyright violation/copy and paste
The "Fake DNA" section in this article is exactly the same to a section here: http://www.bio-medicine.org/biology-definition/Genetic_fingerprinting/#Fake_DNA_evidence. May be other copy-pastes. Tarthen Brown (talk) 10:31, 13 May 2008 (UTC)

Found one: In Cases on OJ Simpson - these two are the same more or less. Who copied who? Tarthen Brown (talk) 10:33, 13 May 2008 (UTC)

Crime work
Given a sample of DNA, what information can we currently know? I guess that technically we should be able to rebuild a person from their DNA. As it stands, what can we do? Can we determine hair colour, eye colour, ethnicity, etc? Or do we just get a complex code that we try to match with another piece of code, kind of like playing the card game snap? Declan Davis (talk) 20:26, 19 September 2008 (UTC)

Chimera (genetics)
DNA is not 100% accurate all the time. Please add information and reference Chimera (genetics) A Chimera has 2 sets of different DNA. Blood could be one and skin could be differant. —Preceding unsigned comment added by 24.255.120.218 (talk) 06:08, 3 August 2008 (UTC)


 * I guess that DNA is always accurate. It's our means of collection and analysis that aren't always 100% accurate. Declan Davis (talk) 20:28, 19 September 2008 (UTC)

Chimera confusion in lead
From the lead:


 * "These loci are variable enough that two unrelated humans are unlikely to have the same alleles, the only exception being the rare individuals which have two different sets of chimeric genes."

This is not an "exception" to that rule, but an extension of it: a chimera is not more likely to have the same alleles as someone unrelated to the chimera.

I am correcting the lead, accordingly. If you object, please discuss in this section and/or cite reliable references that support the claim.

Thank you. &mdash;Danorton (talk) 18:00, 4 October 2008 (UTC)

Identifying ancient, deceased individuals
I have heard of extracting DNA from the fingerprints of the Ancient Egyptian laborers responsible for building the tombs. This is because fats and oils (such as sebum), along with salts and sweat, are exuded from the fingers and hands, and deposited on those objects they happened to touch. This happened thousands of years ago, back when the great pyramids were first built. The fingerprints were sealed up, and left untouched for thousands of years.

Does anybody have more information on this?


 * The fats and oils usually deposited in fingerprints are naturally subject to degradation with time, and because DNA is a protein, usually wanting in the oils exuded by the skin, that rules out DNA fingerprinting. But since the Ancient Egyptian laborers had to manage large blocks of stone by cutting, sliding, and rolling, some of those fingerprints may have been bloody, and that was where the researchers managed to get their DNA.

DNA is not a protein. It is a nucleic acid. They are completely different categories of biomolecules. Whoever is going around dispensing information about DNA, without even knowing what it is, needs to cut it out.

Proteins are polymers of amino acids, which have a carbon center, carboyl, amino and -H termini, and a disctinctive side chain known generically as "-R." Nucleic acids have a sugar-phosphate backbone, to which are attached nitrogenous bases. 165.176.123.2 (talk) 19:59, 28 February 2008 (UTC)


 * I agree, and it's jolly annoying that whoever is giving out this false information doesn't even have the manners to sign their posts. Declan Davis (talk) 20:33, 19 September 2008 (UTC)

betch!!! hoe scum bag!! —Preceding unsigned comment added by 70.231.240.67 (talk) 00:50, 9 October 2008 (UTC)

How long does it take?
The article could use expert input on how long each of the DNA analysis methods takes to get results. There is no mention of it here, and there seems to be much confusion among the public on this issue. I often hear comments from people on the radio or from acquaintances that indicate that they think it's as fast as blood typing and cross-matching (minutes to hours), though from what I recall hearing some years ago, it typically takes several weeks to get results. &mdash;QuicksilverT @ 00:56, 9 October 2008 (UTC)
 * The article could use expert editing, but expert input into the article is contrary to Wikipedia policy. (See WP:NOR). Anyone is welcome to research that information from reliable secondary sources and include it here. If you're unsure, post the information here first for feedback. Experts can then judge the reliability of the source. &mdash;Danorton (talk) 15:31, 9 October 2008 (UTC)
 * If you're talking about just doing the lab work, it is about a half day's work with current STR techniques. You'd go from some kind of sample, say a blood stain on a shirt, cut a portion of that and extract the DNA from the cells on the fabric using PCI, total time ~20 mins.  Next you'd go to quantification of your extracted DNA -- a simple, rough estimate can be performed with a fluorescent method in about 5 minutes.  Next the extracted DNA would be taken for preparation for amplification by PCR, total setup time about 5 minutes as well.  A standard amplification takes roughly 3.5 hrs, then preparation/running on a CE instrument for roughly 1 hr.  Just like that, you've gone from sample to genotype in about 5 hrs of work.  The reason labs take so much longer to get results out is that in the forensic process, steps like accurately documenting evidence for future trial or chain of custody issues are time consuming and do not produce any of the required lab work for generating a profile.  After a genotype has been obtained, it still needs to be interpreted by a DNA analyst, then those results need to be reviewed by other analysts and reviewers to make sure that everything was done correctly before any kind of results can be released to law enforcement or the public.  Unlike TV shows such as CSI, most crime labs cannot clear their plates and devote 100% of their time and effort to a single case as it comes through the door.  So while it's not as fast as simple blood typing, it's not necessarily as slow as you might think. Sekiyu (talk) 07:04, 14 April 2009 (UTC)

Phantom of Heilbronn
There is a interesting case in germany where DNA fingerprinting led to the "construction" of a suspected female serial killer attributed with 40 crimes including several cases of murder. It turned out recently that the DNA traces originally attributed to the suspected killer is that of a woman working in the plant that produced the cotton buds used by the police for sampling the DNA at the crime scene. Maybe anyone can make something out of it. My english is'nt goog enough to edit here and i dont have an account here anyway. 88.128.52.77 (talk) 22:52, 27 March 2009 (UTC)
 * That story is indeed awesome, however I don't think it really adds to this article in a meaningful way, other than cautioning that negative or substrate controls should be run regularly (this is good scientific practice in general, not just in forensics labs). Sekiyu (talk) 07:22, 14 April 2009 (UTC)

DNA profiling vs Full_genome_sequencing
Whats the diffence between DNA profiling and Full_genome_sequencing ? Is it the same? If so, the 2 pages can be merged 81.246.169.193 (talk) 07:37, 20 April 2009 (UTC)

other names
other names are DNA fingerprint and idiosyncratic minisatellite hypervariation profile. Include in article —Preceding unsigned comment added by 81.246.164.113 (talk) 06:56, 21 April 2009 (UTC)

Familial DNA Database Searches
I'm currently working on a draft of a potential article expanding the section on Familial DNA database searches, which are now being used by a greater number of states and are in the media more these days. I hope to include the history of its use, how the searches operate, and an example of how they've been used in a criminal trial, plus some cases around the country, like the Grim Sleeper case where it was used. It may also help clarify the partial match question below, since familial searches are similar to partial matches but NOT the same because they employ a seperate computer program and then YSTR analysis. The information on the familial DNA is probably large enough to have its own Wiki Page- should it be its own page or should it be added to the current familial searching page? Spu2011 Spu2011 (talk) 22:59, 20 April 2011 (UTC) — Preceding unsigned comment added by Spu2011 (talk • contribs) 17:03, 20 April 2011 (UTC)

Osama
Don't forget to add what you can find out about using his dead sister's DNA to identify Osama after they killed him. Make sure to emphasize how they could do it so fast. 4.249.63.135 (talk) 15:22, 2 May 2011 (UTC)

artificial dna
Please, could this be integrated? (I am no expert): http://science.slashdot.org/story/09/08/18/0043212/Scientists-Learn-To-Fabricate-DNA-Evidence --91.37.35.170 (talk) 14:55, 18 August 2009 (UTC)

How to make working model on dna fingerprinting —Preceding unsigned comment added by 59.95.97.121 (talk) 07:50, 10 September 2009 (UTC)


 * I am not an expert either, but am an interested layperson, and I will try to put together a section on this matter.  Anyone here interested in helping?  Pv86 (talk) 19:53, 15 January 2010 (UTC)


 * I've edited it a bit for tone--I do feel that this is something that belongs in the article, but an encyclopedia shouldn't tell people what is "frightening" or "distressing". It still has the "story telling" voice which makes it sound a bit like a news article, but I'm hoping someone who is a little better at writing can make it blend in more seamlessly with the rest of the article. 71.43.182.90 (talk) 02:20, 30 April 2010 (UTC)


 * Section title is misleading. What the researchers were describing is not artificial DNA, but fabrication of DNA evidence by taking DNA from one individual, amplifying it, and planting it into blood/saliva samples of another unrelated person. What is "artificial DNA" anyway? They did not synthesize DNA completely from scratch. 202.92.128.238 (talk) 03:01, 8 February 2012 (UTC)

Considerations when evaluating DNA evidence
The sentence "Because of this, arbitrary ceilings were put on match probabilities used in RFLP analysis than the theoretically computed ones." needs to be cleaned up. "Than" calls for an adjective in the comparative degree - higher ceilings or lower ceilings or stricter limits or whatever.


 * I've fixed this unclear part and added a reference link to more info about the ceiling principle. Sekiyu 16:49, 8 February 2007 (UTC)

The claims about error rates and ceilings are confused and incorrect, and amount to a partisan rendering.
 * 1. The motivation for the ceiling principle (proposed by the 1992 NRC report) was insufficient population data. It had nothing to do with errors.
 * 2. The article by Jonathon Koehler mentioned by the referenced 2002 newspaper article could not have been a reason for moving away from RFLP several years earlier.
 * 3. The reasons for switching from RFLP to STR were increased sensitivity, easier interpretation, and being less labor intensive. I don't recall error rates entering the discussion. Indeed, errors in interpretation is a relatively unimportant component of possible errors, and STRs because of greater sensitivity are more susceptible to error by contamination.
 * 4. Koehler is a psychologist and not a DNA scientist or even statistician. His research scored an error if a lab reported a type of "4.1" when the correct answer was listed as "4" -- for lack of understanding the notation, that "4.1" was not different from "4", but merely more precise, designating a sub-type. Was the study reported in the 2002 newspaper article a different one? Further, despite his assurance to the contrary, his statistical approach is contrived. CharlesBrenner 15:22, 4 July 2007 (UTC)

I'm not sure were it might fit, but would it be worth tying in a reference to the Phantom of Heilbronn in this section? There is recent evidenice suggesting that the DNA matches tying together those 40 crime scenes in Austria, France, and Germany were caused by contamination from the factory makding the cotton buds for DNA swabbing.Occasional Reader (talk) 18:51, 26 March 2009 (UTC)

Isn't the stastical reasoning in regards to coincidental matches flawed? As I understand it, the point is that the chance (risk) of a coincidental match, between two randomly chosen persons, is in theory 1 in 100 bilion...but in reality it is 1 in 1000 - no? At a glance this looks problematic... It seems that it is assumed that there's a probability of 1 against 1000 not only to pick two monozygotic twins, but that they're each other's sibling. Wouldn't the chances of that happening rather be something like 1 in 500.000? And the practical risk then being something in the same neighbourhood (1:500.000,000005 or something like that)? —Preceding unsigned comment added by 212.242.152.183 (talk) 16:27, 28 March 2010 (UTC) Sorry... It would be 1:499.999,999995 - not 1:500.000,000005 :) That is, If I'm correct... I suck at calculating probabilities, so please correct me if I'm wrong... —Preceding unsigned comment added by 212.242.152.183 (talk) 12:08, 29 March 2010 (UTC)

The current (14/3/2011) article states: "For example, the actual probability that 2 random people have the same DNA depends on whether there were twins or triplets (etc.) in the family, and the number of loci used in the test. Where twins are common, the probability of matching the DNA is 22 in 1000, or about 2.2 in 100 will have matching DNA." Which is not referenced and clearly wrong. The tests would not be accepted as evidence if this were the case. I suggest someone adds a proper analysis of the probability of finding an exact match in the profile. I have deleted the prior statement. --TransControl (talk) 08:41, 14 March 2011 (UTC)

There isn't a single citation in for the section Considerations when evaluating DNA evidence. Is anyone even maintaining this page? Indio (talk) 17:04, 3 June 2013 (UTC)

External links modified
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1 in 100 billion?
According to the article, "the theoretical risk of a coincidental match is 1 in 100 billion (100,000,000,000)."

This theoretical risk is almost certainly overoptimistic. See http://www.maa.org/devlin/devlin_09_06.html for more details. This should be noted. 71.102.156.213 00:04, 18 March 2007 (UTC)


 * Thanks for you concern, however it should be noted that this subject is covered in the last subject of this discussion page, titled "Independent Assortment".RSimione 06:38, 7 May 2007 (UTC)


 * You have to consider all factors involved in gametogenesis and fertilization to determine the similarity between chromosomes of siblings. This means mitosis, meiosis (I and II), crossover, mutation, transformation, etc. The probability that two such sequences would result in the same set of chromosomes is absurdly small. Mind  matrix  16:39, 20 February 2016 (UTC)

Dates
First developed and used in 1985

The modern process of DNA profiling was developed in 1988 by Alec Jeffreys.

Are these right? reference 2 says 1984 and 1987. Also reference 2 says its from the observer but it's actually from the guardian.

Nick876436 (talk) 02:12, 17 October 2016 (UTC)

External links modified
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Total rewrite
To anyone watching, I'm going to start rewriting this article and splitting off the forensic aspects into a separate article. DNA profiling encompasses much more than just forensic applications so this article needs to show that. The forensic article will be placed at Forensic DNA analysis. It is currently in draft form and will be published once completed. All are welcome to assist. --Majora (talk) 01:22, 29 October 2017 (UTC)

Case cruft
Thank you for adding the reference to the British titles section. At least now that section has a source that can be used to verify the content (a central Wikipedia policy). What is also a policy here is something called WP:NOT. Specifically Wikipedia is not a list of indiscriminate items. As I tried to get you to see when I linked to the essay on list cruff. It isn't about removing other people's work. It is about following Wikipedia policy as set by community consensus. Not all material is appropriate for inclusion in Wikipedia and a pretty random list of cases over a 31 year span is the definition of indiscriminate. Since this is a collaborative project I hope that I can get your thoughts on this matter. --Majora (talk) 18:06, 29 October 2017 (UTC)
 * If you want to delete whole section, please, start discussion (Wikipedia policy)GorgonaJS (talk) 18:24, 29 October 2017 (UTC)
 * I just did start a discussion. Are you going to contribute to it or not? --Majora (talk) 18:33, 29 October 2017 (UTC)

CODIS13/CODIS20
I don't want to touch this page because it is way beyond my skill set so maybe someone else will want to clean up a little issue for me. Under "STR analysis" we have 20 STRs (CODIS20) as the standard in North America without mentioning that this was upgraded from 13 STRs fairly recently (Jan 1, 2017 https://en.wikipedia.org/wiki/Combined_DNA_Index_System.

Under "Mitochondrial analysis" we have "For highly degraded samples, it is sometimes impossible to get a complete profile of the 13 CODIS STRs." This would have been the standard when the article was written but it is now the only mention of CODIS13 so it seems like a contradiction. Should we add a reference to CODIS13 in the first instance? Or maybe remove the mention of 13 STRs in the later?

Thank you

Artfulstitches (talk) 21:22, 28 April 2018 (UTC)

Desperate American interference in this article
There's quite a lot of careful interference in this article to try and claw back a semblance of the idea that DNA-profiling was not developed for use in the UK, but somehow rested upon U.S. science. It didn't. The article is therefore biased. — Preceding unsigned comment added by 86.87.191.180 (talk) 18:27, 27 December 2021 (UTC)

Uncited material in need of citations
I am moving the following uncited material here until it can be properly supported with inline citations of reliable, secondary sources, per WP:V, WP:CS, WP:IRS, WP:PSTS, WP:BLP, WP:NOR, et al. This diff shows where it was in the article. Nightscream (talk) 17:40, 18 January 2022 (UTC)

Background
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 teenage girls 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 a man who had confessed to one of the crimes, and the subsequent conviction of Colin Pitchfork.

...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.

Profiling processes
The process, developed by Glassberg and independently by Jeffreys, begins with a sample of an individual's DNA (typically called a "reference sample"). Reference samples are usually collected through a buccal swab. When this is unavailable (for example, when a court order is needed but unobtainable) other methods may be needed to collect a sample of blood, saliva, semen, vaginal lubrication, or other fluid or tissue from personal use items (for example, a toothbrush, razor) or from stored samples (for example, banked sperm or biopsy tissue). Samples obtained from blood relatives can indicate an individual's profile, as could previous profiled human remains. A reference sample is then analyzed to create the individual's DNA profile using one of the techniques discussed below. The DNA profile is then compared against another sample to determine whether there is a genetic match.

DNA extraction
After the DNA is extracted from the sample, it can be analyzed, whether it is by RFLP analysis or quantification and PCR analysis.

RFLP analysis
The first methods for finding out genetics used for DNA profiling involved RFLP analysis. DNA is collected from cells and cut into small pieces using a restriction enzyme (a restriction digest). This generates DNA fragments of differing sizes as a consequence of variations between DNA sequences of different individuals. The fragments are then separated on the basis of size using gel electrophoresis.

The separated fragments are then transferred on to a nitrocellulose or nylon filter; this procedure is called a Southern blot. The DNA fragments within the blot are permanently fixed to the filter, and the DNA strands are denatured. Radiolabeled probe molecules are then added that are complementary to sequences in the genome that contain repeat sequences. These repeat sequences tend to vary in length among different individuals and are called variable number tandem repeat sequences or VNTRs. The probe molecules hybridize to DNA fragments containing the repeat sequences and excess probe molecules are washed away. The blot is then exposed to an X-ray film. Fragments of DNA that have bound to the probe molecules appear as fluorescent bands on the film.

The Southern blot technique requires large amounts of non-degraded sample DNA. Also, Alec Jeffrey's original multilocus RFLP technique looked at many minisatellite loci at the same time, increasing the observed variability, but making it hard to discern individual alleles (and thereby precluding paternity testing). These early techniques have been supplanted by PCR-based assays.

Polymerase chain reaction (PCR) analysis
Developed by Kary Mullis in 1983, a process was reported by which specific portions of the sample DNA can be amplified almost indefinitely (Saiki et al. 1985, 1986). The process, polymerase chain reaction (PCR), mimics the biological process of DNA replication, but confines it to specific DNA sequences of interest. With the invention of the PCR technique, DNA profiling took huge strides forward in both discriminating power and the ability to recover information from very small (or degraded) starting samples.

PCR greatly amplifies the amounts of a specific region of DNA. In the PCR process, the DNA sample is denatured into the separate individual polynucleotide strands through heating. Two oligonucleotide DNA primers are used to hybridize to two corresponding nearby sites on opposite DNA strands in such a fashion that the normal enzymatic extension of the active terminal of each primer (that is, the 3’ end) leads toward the other primer. PCR uses replication enzymes that are tolerant of high temperatures, such as the thermostable Taq polymerase. In this fashion, two new copies of the sequence of interest are generated. Repeated denaturation, hybridization, and extension in this fashion produce an exponentially growing number of copies of the DNA of interest. Instruments that perform thermal cycling are readily available from commercial sources. This process can produce a million-fold or greater amplification of the desired region in two hours or less.

Early assays such as the HLA-DQ alpha reverse dot blot strips grew to be very popular owing to their ease of use, and the speed with which a result could be obtained. However, they were not as discriminating as RFLP analysis. It was also difficult to determine a DNA profile for mixed samples, such as a vaginal swab from a sexual assault victim.

However, the PCR method was readily adaptable for analyzing VNTR, in particular STR loci. In recent years, research in human DNA quantitation has focused on new "real-time" quantitative PCR (qPCR) techniques. Quantitative PCR methods enable automated, precise, and high-throughput measurements. Inter-laboratory studies have demonstrated the importance of human DNA quantitation on achieving reliable interpretation of STR typing and obtaining consistent results across laboratories.

STR analysis
...or short tandem repeats (STR). This method uses highly polymorphic regions that have short repeated sequences of DNA (the most common is 4 bases repeated, but there are other lengths in use, including 3 and 5 bases). Because unrelated people almost certainly have different numbers of repeat units, STRs can be used to discriminate between unrelated individuals. These STR loci (locations on a chromosome) are targeted with sequence-specific primers and amplified using PCR. The DNA fragments that result are then separated and detected using electrophoresis. There are two common methods of separation and detection, capillary electrophoresis (CE) and gel electrophoresis.

Each STR is polymorphic, but the number of alleles is very small. Typically each STR allele will be shared by around 5–20% of individuals. The power of STR analysis derives from inspecting multiple STR loci simultaneously. The pattern of alleles can identify an individual quite accurately. Thus STR analysis provides an excellent identification tool. The more STR regions that are tested in an individual the more discriminating the test becomes.

Whichever system is used, many of the STR regions used are the same. These DNA-profiling systems are based on multiplex reactions, whereby many STR regions will be tested at the same time.

Moreover, since there are about 12 million monozygotic twins on Earth, the theoretical probability is not accurate.

In practice, the risk of contaminated-matching is much greater than matching a distant relative, such as contamination of a sample from nearby objects, or from left-over cells transferred from a prior test. The risk is greater for matching the most common person in the samples: Everything collected from, or in contact with, a victim is a major source of contamination for any other samples brought into a lab. For that reason, multiple control-samples are typically tested in order to ensure that they stayed clean, when prepared during the same period as the actual test samples. Unexpected matches (or variations) in several control-samples indicates a high probability of contamination for the actual test samples. In a relationship test, the full DNA profiles should differ (except for twins), to prove that a person was not actually matched as being related to their own DNA in another sample.

AFLP
Another technique, AFLP, or amplified fragment length polymorphism was also put into practice during the early 1990s. This technique was also faster than RFLP analysis and used PCR to amplify DNA samples. It relied on variable number tandem repeat (VNTR) polymorphisms to distinguish various alleles, which were separated on a polyacrylamide gel using an allelic ladder (as opposed to a molecular weight ladder). Bands could be visualized by silver staining the gel. One popular focus for fingerprinting was the D1S80 locus. As with all PCR based methods, highly degraded DNA or very small amounts of DNA may cause allelic dropout (causing a mistake in thinking a heterozygote is a homozygote) or other stochastic effects. In addition, because the analysis is done on a gel, very high number repeats may bunch together at the top of the gel, making it difficult to resolve. AmpFLP analysis can be highly automated, and allows for easy creation of phylogenetic trees based on comparing individual samples of DNA. Due to its relatively low cost and ease of set-up and operation, AmpFLP remains popular in lower income countries.

DNA family relationship analysis
[[File:Stages of Gene Fingerprinting.svg|thumb|1: A cell sample is taken – usually a cheek swab or blood test

2: DNA is extracted from sample

3: Cleavage of DNA by restriction enzyme – the DNA is broken into small fragments

4: Small fragments are amplified by the polymerase chain reaction – results in many more fragments

5: DNA fragments are separated by electrophoresis

6: The fragments are transferred to an agar plate

7: On the agar plate specific DNA fragments are bound to a radioactive DNA probe

8: The agar plate is washed free of excess probe

9: An x-ray film is used to detect a radioactive pattern

10: The DNA is compared to other DNA samples.]] Using PCR technology, DNA analysis is widely applied to determine genetic family relationships such as paternity, maternity, siblingship and other kinships.

During conception, the father's sperm cell and the mother's egg cell, each containing half the amount of DNA found in other body cells, meet and fuse to form a fertilized egg, called a zygote. The zygote contains a complete set of DNA molecules, a unique combination of DNA from both parents. This zygote divides and multiplies into an embryo and later, a full human being.

At each stage of development, all the cells forming the body contain the same DNA—half from the father and half from the mother. This fact allows the relationship testing to use all types of all samples including loose cells from the cheeks collected using buccal swabs, blood or other types of samples.

There are predictable inheritance patterns at certain locations (called loci) in the human genome, which have been found to be useful in determining identity and biological relationships. These loci contain specific DNA markers that scientists use to identify individuals. In a routine DNA paternity test, the markers used are short tandem repeats (STRs), short pieces of DNA that occur in highly differential repeat patterns among individuals.

Each person's DNA contains two copies of these markers—one copy inherited from the father and one from the mother. Within a population, the markers at each person's DNA location could differ in length and sometimes sequence, depending on the markers inherited from the parents.

The combination of marker sizes found in each person makes up their unique genetic profile. When determining the relationship between two individuals, their genetic profiles are compared to see if they share the same inheritance patterns at a statistically conclusive rate.

For example, the following sample report from this commercial DNA paternity testing laboratory Universal Genetics signifies how relatedness between parents and child is identified on those special markers:

The partial results indicate that the child and the alleged father's DNA match among these five markers. The complete test results show this correlation on 16 markers between the child and the tested man to enable a conclusion to be drawn as to whether or not the man is the biological father.

Each marker is assigned with a Paternity Index (PI), which is a statistical measure of how powerfully a match at a particular marker indicates paternity. The PI of each marker is multiplied with each other to generate the Combined Paternity Index (CPI), which indicates the overall probability of an individual being the biological father of the tested child relative to a randomly selected man from the entire population of the same race. The CPI is then converted into a Probability of Paternity showing the degree of relatedness between the alleged father and child.

The DNA test report in other family relationship tests, such as grandparentage and siblingship tests, is similar to a paternity test report. Instead of the Combined Paternity Index, a different value, such as a Siblingship Index, is reported.

The report shows the genetic profiles of each tested person. If there are markers shared among the tested individuals, the probability of biological relationship is calculated to determine how likely the tested individuals share the same markers due to a blood relationship.

Y-chromosome analysis
Recent innovations have included the creation of primers targeting polymorphic regions on the Y-chromosome (Y-STR), which allows resolution of a mixed DNA sample from a male and female or cases in which a differential extraction is not possible. Y-chromosomes are paternally inherited, so Y-STR analysis can help in the identification of paternally related males. Y-STR analysis was performed in the Jefferson-Hemings controversy to determine if Thomas Jefferson had sired a son with one of his slaves.

The analysis of the Y-chromosome yields weaker results than autosomal chromosome analysis with regard to individual identification. The Y male sex-determining chromosome, as it is inherited only by males from their fathers, is almost identical along the paternal line. On the other hand, the Y-STR haplotype provides powerful genealogical information as a patrilinear relationship can be traced back over many generations.

Mitochondrial analysis
For highly degraded samples, it is sometimes impossible to get a complete profile of the 13 CODIS STRs. In these situations, mitochondrial DNA (mtDNA) is sometimes typed due to there being many copies of mtDNA in a cell, while there may only be 1–2 copies of the nuclear DNA. Forensic scientists amplify the HV1 and HV2 regions of the mtDNA, and then sequence each region and compare single-nucleotide differences to a reference. Because mtDNA is maternally inherited, directly linked maternal relatives can be used as match references, such as one's maternal grandmother's daughter's son. In general, a difference of two or more nucleotides is considered to be an exclusion. Heteroplasmy and poly-C differences may throw off straight sequence comparisons, so some expertise on the part of the analyst is required. mtDNA is useful in determining clear identities, such as those of missing people when a maternally linked relative can be found. mtDNA testing was used in determining that Anna Anderson was not the Russian princess she had claimed to be, Anastasia Romanov.

Degraded DNA
In the real world DNA labs often have to deal with DNA samples that are less than ideal. DNA samples taken from crime scenes are often degraded, which means that the DNA has started to break down into smaller fragments. Victims of homicides might not be discovered right away, and in the case of a mass casualty event it could be hard to get DNA samples before the DNA has been exposed to degradation elements.

Degradation or fragmentation of DNA at crime scenes can occur because of a number of reasons, with environmental exposure often being the most common cause. Biological samples that have been exposed to the environment can get degraded by water and enzymes called nucleases. Nucleases essentially ‘chew’ up the DNA into fragments over time and are found everywhere in nature.

In terms of a forensic approach to a degraded DNA sample, STR loci STR analysis are often amplified using PCR-based methods. Though STR loci are amplified with greater probability of success with degraded DNA, there is still the possibility that larger STR loci will fail to amplify, and therefore, would likely yield a partial profile, which results in reduced statistical weight of association in the event of a match.

MiniSTR Analysis
In this case the fire at destroyed the DNA samples so badly that normal STR testing did not result in a positive identification of some of the victims.

DNA mixtures
Probabilistic genotyping software that are often used in labs today include STRmix and TrueAllele.

Considerations when evaluating DNA evidence
As DNA profiling became a key piece of evidence in the court, defense lawyers based their arguments on statistical reasoning. For example: Given a match that had a 1 in 5 million probability of occurring by chance, the lawyer would argue that this meant that in a country of say 60 million people there were 12 people who would also match the profile. This was then translated to a 1 in 12 chance of the suspect's being the guilty one. This argument is not sound unless the suspect was drawn at random from the population of the country. In fact, a jury should consider how likely it is that an individual matching the genetic profile would also have been a suspect in the case for other reasons. Also, different DNA analysis processes can reduce the amount of DNA recovery if the procedures are not properly done. Therefore, the number of times a piece of evidence is sampled can diminish the DNA collection efficiency. Another spurious statistical argument is based on the false assumption that a 1 in 5 million probability of a match automatically translates into a 1 in 5 million probability of innocence and is known as the prosecutor's fallacy.

RFLP heventualy fell into disuse due to the advent of more discriminating, sensitive and easier technologies.

Since 1998, the DNA profiling system supported by The National DNA Database in the UK is the SGM+ DNA profiling system that includes 10 STR regions and a sex-indicating test. STRs do not suffer from such subjectivity and provide similar power of discrimination (1 in 1013 for unrelated individuals if using a full SGM+ profile). Figures of this magnitude are not considered to be statistically supportable by scientists in the UK; for unrelated individuals with full matching DNA profiles a match probability of 1 in a billion is considered statistically supportable. However, with any DNA technique, the cautious juror should not convict on genetic fingerprint evidence alone if other factors raise doubt. Contamination with other evidence (secondary transfer) is a key source of incorrect DNA profiles and raising doubts as to whether a sample has been adulterated is a favorite defense technique. More rarely, chimerism is one such instance where the lack of a genetic match may unfairly exclude a suspect.

Evidence of genetic relationship
This happens when two eggs are fertilized at the same time and fuse together to create one individual instead of twins.

Fake DNA evidence
In one case, a criminal planted fake DNA evidence in his own body: John Schneeberger raped one of his sedated patients in 1992 and left semen on her underwear. Police drew what they believed to be Schneeberger's blood and compared its DNA against the crime scene semen DNA on three occasions, never showing a match. It turned out that he had surgically inserted a Penrose drain into his arm and filled it with foreign blood and anticoagulants.

In the case of the Phantom of Heilbronn, police detectives found DNA traces from the same woman on various crime scenes in Austria, Germany, and France—among them murders, burglaries and robberies. Only after the DNA of the "woman" matched the DNA sampled from the burned body of a male asylum seeker in France did detectives begin to have serious doubts about the DNA evidence. It was eventually discovered that DNA traces were already present on the cotton swabs used to collect the samples at the crime scene, and the swabs had all been produced at the same factory in Austria. The company's product specification said that the swabs were guaranteed to be sterile, but not DNA-free.

Familial DNA searching
To eliminate the majority of this list when the forensic DNA is a man's, crime lab technicians conduct Y-STR analysis. Using standard investigative techniques, authorities are then able to build a family tree. The family tree is populated from information gathered from public records and criminal justice records. Investigators rule out family members' involvement in the crime by finding excluding factors such as sex, living out of state or being incarcerated when the crime was committed. They may also use other leads from the case, such as witness or victim statements, to identify a suspect. Once a suspect has been identified, investigators seek to legally obtain a DNA sample from the suspect. This suspect DNA profile is then compared to the sample found at the crime scene to definitively identify the suspect as the source of the crime scene DNA.

Other states are expected to follow.

Regardless of whether familial DNA searching was the method used to identify the suspect, authorities always conduct a normal DNA test to match the suspect's DNA with that of the DNA left at the crime scene.

Using publicly available records, the investigators created a family tree. They then eliminated all the family members who were incarcerated at the time of the offense, as well as all of the females (the crime scene DNA profile was that of a male). Investigators obtained a court order to collect the suspect's DNA, but the suspect actually volunteered to come to a police station and give a DNA sample. After providing the sample, the suspect walked free without further interrogation or detainment. Later confronted with an exact match to the forensic profile, the suspect pleaded guilty to criminal trespass at the first court date and was sentenced to two years probation.

In Italy a familiar DNA search has been done to solve the case of the murder of Yara Gambirasio whose body was found in the bush three months after her disappearance. A DNA trace was found on the underwear of the murdered teenage near and a DNA sample was requested from a person who lived near the municipality of Brembate di Sopra and a common male ancestor was found in the DNA sample of a young man not involved in the murder. After a long investigation the father of the supposed killer was identified as Giuseppe Guerinoni, a deceased man, but his two sons born from his wife were not related to the DNA samples found on the body of Yara. After three and a half years the DNA found on the underwear of the deceased girl was matched with Massimo Giuseppe Bossetti who was arrested and accused of the murder of the 13-year-old girl. In mid-2016 Bossetti was found guilty and sentenced to life by the Corte d'assise of Bergamo.

Partial matches
Hunt was exonerated in 2004 when a DNA database search produced a remarkably close match between a convicted felon and the forensic profile from the case. The partial match led investigators to the felon's brother, Willard E. Brown, who confessed to the crime when confronted by police. A judge then signed an order to dismiss the case against Hunt. In Italy, partial matching has been used in the controversial murder of Yara Gambirasio, a child found dead about a month after her presumed kidnapping. In this case, the partial match has been used as the only incriminating element against the defendant, Massimo Bossetti, who has been subsequently condemned for the murder (waiting appeal by the Italian Supreme Court).

England and Wales
Phillips LJ gave this example of a summing up, which should be carefully tailored to the particular facts in each case:

"Members of the Jury, if you accept the scientific evidence called by the Crown, this indicates that there are probably only four or five white males in the United Kingdom from whom that semen stain could have come. The Defendant is one of them. If that is the position, the decision you have to reach, on all the evidence, is whether you are sure that it was the Defendant who left that stain or whether it is possible that it was one of that other small group of men who share the same DNA characteristics."

Cases

 * In 1988, Timothy Wilson Spencer was the first man in Virginia to be sentenced to death through DNA testing, for several rape and murder charges. He was dubbed "The South Side Strangler" because he killed victims on the south side of Richmond, Virginia. He was later charged with rape and first-degree murder and was sentenced to death. He was executed on 27 April 1994. David Vasquez, initially convicted of one of Spencer's crimes, became the first man in America exonerated based on DNA evidence.
 * In 1989, Chicago man Gary Dotson was the first person whose conviction was overturned using DNA evidence.
 * In 1991, Allan Legere was the first Canadian to be convicted as a result of DNA evidence, for four murders he had committed while an escaped prisoner in 1989. During his trial, his defense argued that the relatively shallow gene pool of the region could lead to false positives.
 * In 1992, DNA evidence was used to prove that Nazi doctor Josef Mengele was buried in Brazil under the name Wolfgang Gerhard.
 * In 1993, Kirk Bloodsworth was the first person to have been convicted of murder and sentenced to death, whose conviction was overturned using DNA evidence.
 * The 1993 rape and murder of Mia Zapata, lead singer for the Seattle punk band The Gits, was unsolved nine years after the murder. A database search in 2001 failed, but the killer's DNA was collected when he was arrested in Florida for burglary and domestic abuse in 2002.
 * The science was made famous in the United States in 1994 when prosecutors heavily relied on DNA evidence allegedly linking O. J. Simpson to a double murder. The case also brought to light the laboratory difficulties and handling procedure mishaps that can cause such evidence to be significantly doubted.
 * In 1994, Royal Canadian Mounted Police (RCMP) detectives successfully tested hairs from a cat known as Snowball, and used the test to link a man to the murder of his wife, thus marking for the first time in forensic history the use of non-human animal DNA to identify a criminal (plant DNA was used in 1992, see above).
 * [Earl Washington, Jr]'s His case is often cited by opponents of the death penalty.
 * In 1995, the British Forensic Science Service carried out its first mass intelligence DNA screening in the investigation of the Naomi Smith murder case.
 * In 1998, Richard J. Schmidt was convicted of attempted second-degree murder when it was shown that there was a link between the viral DNA of the human immunodeficiency virus (HIV) he had been accused of injecting in his girlfriend and viral DNA from one of his patients with AIDS. This was the first time viral DNA fingerprinting had been used as evidence in a criminal trial.
 * In 2002, DNA testing was used to exonerate Douglas Echols, a man who was wrongfully convicted in a 1986 rape case. Echols was the 114th person to be exonerated through post-conviction DNA testing.
 * [Welshman Jeffrey Gafoor case] This may be the first known example of the DNA of an innocent yet related individual being used to identify the actual criminal, via "familial searching".
 * In March 2003, Josiah Sutton was released from prison after serving four years of a twelve-year sentence for a sexual assault charge. Questionable DNA samples taken from Sutton were retested in the wake of the Houston Police Department's crime lab scandal of mishandling DNA evidence.
 * The three men had already served eighteen years of their thirty-plus-year sentences.
 * The trial of Robert Pickton (convicted in December 2003) is notable in that DNA evidence is being used primarily to identify the victims, and in many cases to prove their existence.
 * In December 2005, Evan Simmons was proven innocent of a 1981 attack on an Atlanta woman after serving twenty-four years in prison. Mr. Clark is the 164th person in the United States and the fifth in Georgia to be freed using post-conviction DNA testing.
 * In 2019, dismembered remains found in a cave in Idaho in 1979 and 1991 were identified through genetic fingerprinting as belonging to Joseph Henry Loveless. Loveless was a habitual criminal who had disappeared after escaping from jail in 1916, where he had been charged with killing his wife Agnes with an axe. Clothes found with the remains matched the description of those Loveless was wearing when he made his escape.

Oligos
I added a link to oligos because the term is used only once, and without definition. As a layperson, I didn't feel confident enough to add a definition, but I think there should be a short one, as per MOS:NOFORCELINK—after all, I had to look it up in order to understand the sentence. Matuko (talk) 05:34, 11 June 2022 (UTC)

Garbled text
This appears to be garbled: "This led Plebuch to conduct an extensive investigation, after which she concluded that he father had been switched ...". AlanS1951 (talk) 10:12, 18 August 2021 (UTC)
 * It took almost a year, but I've corrected it. In future you should feel free to just go ahead and boldly correct something like that as soon as you see it. Typos are considered to be minor edits and don't need consensus. Matuko (talk) 14:09, 11 June 2022 (UTC)

Sir Alec Jeffries?
"Discovered by Sir Alec Jeffreys in 1984" - he was not Sir Alec at the time of the discovery. I am not sure what Wikipedia style is here but I think it make sense to lose the 'Sir.' Cross Reference (talk) 01:07, 4 August 2022 (UTC)


 * I think it should be removed. See also MOS:PREFIX and MOS:SIR. Mind  matrix  12:15, 4 August 2022 (UTC)

Wiki Education assignment: Molecular Genetics
— Assignment last updated by Primashailes2022 (talk) 03:13, 12 September 2022 (UTC)

Wiki Education assignment: Senior Seminar
— Assignment last updated by Acsieling (talk) 18:24, 1 March 2023 (UTC)

1984 or 1985?
I was looking at the background portion of the article and noticed a discrepancy between the article and my research. My sources show that Jefferys made the first discovery about DNA profiling and typing in 1985 instead of 1984. When I looked into the source used in the article that provided the 1984 date, I found that it was an article by The Guardian. I couldn't find which sources The Guardian used to find that information; however, after reading part of the article I also discovered that, according to The Guardian, Jefferys didn't develop the process for DNA profiling in 1984, rather in September of 1984, he had completed a phase of research on how inherited illnesses pass between families. I don't think The Guardian is a reliable enough source for a date such as this. Here is the link for the resource/journal article I have been using: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7219171/

If I don't hear a response from anyone on this discrepancy, I'm going to move forward with making the change and updating the sources. Zalula01 (talk) 14:25, 15 April 2023 (UTC)