MBA DNA Consulting, LLC - Los Angeles, CA

Forensic DNA Consulting Blog


My friend and recent DNA Interview Series guest, Anjali B. Dooley (anjalilawoffice.com, sidebartv.com) and I have been discussing the intersection of attorneys and experts.  We have decided to do a collaboratorive posting about understanding DNA reports  in criminal cases.  Based on the material I have posted here, she will be offering additional commentary and questions from the attorney perspective (see comments section).

Basic Technologies   

credit: beltina.org
credit: beltina.org

 Autosomal STR DNA testing is the most common method used in criminal cases.  It assesses DNA variation present on non-sex determining chromosomes.  In plain English, it detects both male and female DNA.  Autosomal STR DNA testing is the garden variety method which can produce DNA profiles with sufficient information to provide an impressive discrimination power between individuals.  It is not uncommon for expected population frequencies of DNA profiles to boast numbers such as ‘1 in a quadrillion’ (1 in 1,000,000,000,000,000).

Y STR DNA testing is becoming more prevalent in forensic DNA laboratories.  It exclusively detects male DNA by focusing on areas on the Y chromosome. It is particularly useful for samples that contain trace amounts of male DNA mixed with large concentrations of female DNA which can effectively swamp out the male DNA present during autosomal STR DNA testing.

Examples of situations in which Y STR testing is helpful: 

-male digital penetration of vagina 

The amount of DNA transferred from skin cells and perspiration on the finger is relatively low compared to the cellular-rich environment of the vagina.

 –semen from a vasectomized male in a vagina 

A vast majority of the DNA content in semen is found in the sperm cells.  The semen of vasectomized males will have some DNA, but in very low concentration compared to the DNA present in a vagina.

In situations such as these, Y STR DNA testing is helpful since it ignores the female DNA present and provides information on the male DNA present.  However, there is a price to be paid.  Y STR DNA profiles are nowhere near as discriminating as autosomal STR DNA profiles and are consistent within a paternal lineage.  A Y STR DNA profile said to be consistent with a suspect might be expected to occur with a frequency of 1 in a few thousand individuals and is indistinguishable from the biological father or brother of the suspect.

DNA Discovery-Getting the Full Picture

The forensic DNA reports generated by crime laboratories are seldom user friendly for defense attorneys.  Forensic DNA testing is highly complex and sensitive and requires rigorous interpretation.  It is not clinical-type testing in which the testing provides simple “positive” and “negative” results.

Tip of the Iceberg
credit: the-tip-of-my-iceberg.tumblr.com

When encountering reports from either autosomal STR DNA testing or Y STR DNA testing, perhaps the most important point to bear in mind is that the DNA report itself is only the tip of the iceberg. 

Thorough DNA discovery is necessary to determine whether:  protocols were adhered to, the actual raw results support the conclusions, there are any quality issues with the testing or analysts, sufficient documentation of the process exists, and statistical corrections are appropriate.

Examples of information that may not be included in DNA reports: 

-whether or not contamination or other problems occurred during testing 

-names of all analysts involved in the testing process 

-appearance and size of samples and stains 

-sampling technique used 

-exact levels of DNA detected 

-complete chain of custody information 

-reasoning behind any assumptions made in the interpretations 

-specific interpretation guidelines

An effective DNA discovery request needs to be highly specific and void of boiler plate ‘fluff’ that merely creates busy work for the laboratory. Essential components of a DNA discovery request include:  laboratory bench notes, CV and proficiency test results for analysts, QC reports (e.g. contamination instances, corrective actions, and unexpected results), raw electronic STR DNA data, protocols for all analyses, interpretation guidelines, the Quality Assurance Manual, and complete chain of custody information.

Whether or not you have a DNA expert on your case, simply obtaining the final DNA report is not sufficient due diligence. Further discovery is essential to understanding the full impact of the DNA testing on your case. Unfortunately, both prosecutors and defense attorneys do not always realize this.

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Comments 24

  1. author Anjali Dooley posted December 7th 2012. 5:34 pm

    Hi Mehul! Thanks for informing us all on the different types of DNA. This will assist my clients greatly! However, I wanted to followup on this topic and maybe you could give me some additional feedback for my criminal defense clients.

    I know you gave the information, but how would a good criminal defense attorney use this information? Why? What’s good and bad about this type of DNA sampling? What are common mistakes that can happen? Can you explain this as if I was a lay person?

    My clients are often scared when they come into my office. They often state that Ms.Dooley, they will not find DNA, but often I reply “even with the lack of DNA, a conviction can occur”…has this happened to you in any of your cases where you were an expert? I appreciate your feedback and can’t wait to follow-up on this regularly! Your post will be reposted on SIDEBARTV.com and AnjaliLawOffice.com!

  2. author dnadmin posted December 8th 2012. 11:39 am


    A few things come to mind:

    -the question of DNA being found versus incriminating DNA being found
    -the old adage “absence of evidence is not evidence of absence”
    -reasons why DNA may or may not have been recovered
    -all DNA associations are not alike

    These types of questions are often really independent of the quality of the DNA laboratory testing, they are more a question of the context of the results in the case. Of course in discovery, we are looking for out and out errors, but more often it is to gain insight into these other issues.

    Most of the DNA test results introduced into court cases are from automsomal (garden variety) DNA testing kits such as Identifiler, Profiler Plus/COfiler, and PowerPlex 16. Although this type of DNA testing is inherently more powerful than Y STR testing, some of the results can be very ambiguous. If there is an incomplete result with a mixture of individuals, you may get inclusions of individuals and an associated statistic of 1 in 20! The jury needs to know the difference between this type of weak association and a full DNA match. In other words, all DNA associations are not alike!

    Y STR testing is considered the testing of last resort. In other words, it’s better than nothing. If you are dealing with a Y STR case there is a far less power of association possible between a suspect and a piece of evidence. Again, a jury may just hear ‘DNA’ and think it is a mystical, magic bullet.

    DNA found on the hands of a male suspect accused of say groping and attempted digital penetration of a female victim is a good example of grey area in DNA testing. Since we are not dealing with blood or semen DNA on the suspect’s hands, there is likely no way to identify the cellular origin of any victim’s DNA on his hands. For example, there is no test to tell us that vaginal fluid is the source of any female DNA on his hands. Obviously, a hug or handshake can transfer DNA from the victim to the suspect’s hands. What does it mean if a DNA test of the suspect’s hands reveals victim’s DNA? What if no DNA is found?

    If no DNA is found, the prosecution may argue that it is possible to touch someone and not get their DNA on your hand, or that as time has passed it is less likely that DNA will survive on the hand. The defense would argue that it is very easy to transfer DNA and laboratories have an array of highly sensitive tests that are likely to detect even minute transfers. I always like to point out that despite a sterile environment, training, gloves, masks, etc. contamination happens even in the controlled environment of the best DNA laboratories. Clearly DNA can be easily transferred.

    In summary, DNA is rightfully lauded as a powerful forensic tool in large part due to its ability to associate an individual with a piece of evidence with large statistical significance. However, because the testing is sensitive and there are emerging techniques such as YSTR testing, many times the results are ambiguous based on mixtures and less than impressive statistics, or even the context of the case.

    The defense attorney must make sure that less than impressive DNA evidence does not awe the jury simply because it is “DNA”.

    On the flipside (and I hate the over-used term “CSI effect”!) jurors demand DNA testing if at all possible. As a defense attorney, you must take the prosecution to task if there was a case where DNA could have been used but was not, particularly if the only excuse is ‘budget’!

    I can recall a grand theft auto case in which a suspect adamantly denied being involved. The law enforcement agency had collected a swab of the interior driver’s door handle, but never analyzed it. I performed DNA testing on that swab and detected a nice amount of DNA revealing a mixture of at least 2 individuals. The suspect was excluded and the defense attorney prevailed.

    • author Anjali Dooley posted December 11th 2012. 7:28 am

      Mehul, that was a lot of great information! As a defense attorney, my clients often have budget constraints and cannot get DNA testing performed, especially in some of the rural areas I practice in. The prosecution also has a limited budget and does not perform proper testing even if DNA issues are present. So as a defense attorney I am left with questioning the victim, and making them look “bad” or a liar, make sure their credibility is shot. This works 50% of the time. Since you are a DNA expert, can you give my clients the information on how much the different types of DNA testing you described costs? Have you seen organizations that help criminal defense organizations obtain DNA tests and experts at a lower cost?

  3. author dnadmin posted December 11th 2012. 9:25 am

    Great question Anjali,

    If you do an internet search for DNA testing labs, you will find many labs with varied pricing. In my opinion, for criminal matters it is best to use a lab that is accredited by either ASCLD-LAB International or FQS-I. You will pay the price for these accreditations, but you want to go into court with test results that have as much clout as possible.

    Are there excellent DNA labs that are not accredited? Of course. Is accreditation the be-all, end-all? Nope. Do accredited labs sometimes have issues? Of course, but using a laboratory that is not accredited, opens you up to a courtroom attack-particularly since presumably the prosecution’s lab is accredited.

    The pricing for both autosomal STR and Y STR testing is pretty similar. Ballpark..count on about $1,100 per sample for a thorough forensic analysis and report. Keep in mind that you may also require testimony from the lab analyst, so geography of the lab is important for travel costs.

    If perhaps all you need to do is test or re-test a known, reference sample from an individual you are likely looking at about $500 per sample.

    Be sure to thoroughly discuss your case with the lab so that the most accurate pricing is offered for the particular scope and goal of the testing in your case. Defense attorneys should negotiate with the laboratory for pricing, perhaps leveraging the prospect of an ongoing relationship.

    Unfortunately I am not aware of organizations that can help with reduced pricing. In the case of indigent clients of course, the court may pick up the tab. However, budgets are tight and judges will want a convincing argument for the testing. You may need to enlist a DNA expert to write a declaration backing up the testing request.

  4. author Njee posted December 24th 2012. 11:20 pm

    In a framed rape case defence asked for DNA test and report said that ” No DNA could not be extrcated from the sample to match with the provided sample DNA (acqused DNA)”
    what does it means ? Can it help the accused anaway and how court will take it ?

    • author dnadmin posted December 27th 2012. 3:09 pm

      Hello Njee,

      Thank you for submitting your question. It sounds like there is no DNA evidence tying the accused to the crime. Many questions arise from this. It depends on the sample type, how it was stored, and how long after the incident it was obtained. Depending on context, the finding of no DNA could actually point to no sexual contact. Of course, the old adage applies ‘absence of evidence is not evidence of absence’.

      It is important to find out why DNA could not be extracted. I look at negative DNA reports just as closely as reports with reported DNA results. Was there DNA evidence found that is favorable to the accused, but was not reported? Could further work have been done to obtain a result? Is there remaining sample for a re-test? Is there an error in the testing process that resulted in no results being obtained?

      These are some of the considerations and questions that arise based on the limited description you have provided of the scenario.

      • author Njee posted December 28th 2012. 2:04 am

        Thanks for reply.

        Actually, nothing more is written in DNA report and practically it is not possiable for us to ask these questions and get the answer from lab. But does is it indicate absence of semen in rape kit ?

        • author dnadmin posted December 28th 2012. 9:03 am

          Hi Njee,

          To me the phrase “No DNA could not be extracted from the sample to match with the provided DNA sample DNA (accused DNA)” means either: no DNA at all was recovered from the sample, or….the DNA extracted from the sample did not match the accused. I tend to think it means that they recovered no DNA at all. At any rate, with either interpretation, there is no DNA evidence tying the accused to the sample. Feel free to fax or email me the report if you like.

        • author Anjali B. Dooley posted December 28th 2012. 9:36 pm

          However, even though there is no DNA tying the accused to the rape doesn’t mean the totality of evidence won’t convict the defendant. Be careful on the use of lack of DNA present—it is quite convincing for exoneration, but make sure that the totality of the evidence is tied together.

  5. author Sello Phihlela posted May 13th 2013. 5:39 am

    I am a practising attorney based in South Africa where the use of DNA testing is only now becoming prevalent especially in rape cases. I have always been fascinated with the value attached to DNA evidence in court and have often wondered whether there is a global standard of competency and/or consistency required in every instance where DNA is extracted for testing. I understand from your comments above that some degree of contamination or DNA transfer will invariably occur in everyday parlance as such i would like to know what are the accepted standards expected of a DNA testing laboratory in terms of their testing protocols, contamination detection and mitigation, quality assurance, analysts proficiency, false data integrity detection systems, interpretation guidelines etcetera. A check list would prove most helpful if any. Thank you in advance.

    • author dnadmin posted May 13th 2013. 3:50 pm

      Greetings Sello,

      Thank you for your stopping by the blog and for your inquiry.

      Let me start my providing an idea of items that should be requested in discovery in any case dealing with DNA. A defense expert will want to review:
      -all lab notes, reports, data, communication logs, chain of custody information, CODIS hit reports, notes from evidence collection screening and preservation
      -CV of analysts involved
      -Proficiency test results for analysts involved
      -Any documentation of QC issues in the case such as contamination logs, corrective actions, discrepancy reports, unexpected results, and similarly titled documents.
      -CDs containing all electronic data necessary to re-create the STR data analysis performed
      -quality assurance manual
      -forensic biology/DNA examination and testing protocols
      -interpretation guidelines for the specific typing kit used
      -analysis parameters used for electronic data analysis/genotyping
      -mixture interpretation guidelines

      First and foremost it has to be determined if the laboratory followed their own guidelines.

      As far as a global standard, that is a little more difficult to nail down.

      Take a look at the FBI’s Quality Assurance Standards for Forensic DNA Testing Laboratories:

      Accredited DNA laboratories are required to abide by these standards, which are also mandatory for DNA labs participating in FBI’s CODIS database. Each year a laboratory is audited against these standards. Every other year the audit must be done by an external audit team.

      There is an international standard for laboratory testing called the ISO/IEC 17025:2005 ‘General requirements for the competence of testing and calibration laboratories’. DNA laboratories with ISO accreditation must follow these standards. Unfortunately, there is a fee to acquire the ISO standards:

      Accreditation bodies such as ASCLD/LAB will have supplemental standards in addition to the ISO standards:

      Unfortunately, these are not posted online either.
      Feel free to email me directly with further questions as I have previously directed a private DNA laboratory that had ASCLD/LAB-International accreditation and was subject to FBI Quality Assurance audits.

      Other good references are the SWGDAM guidelines for DNA interpretation and laboratory validation.


      Happy Reading!!
      I hope this helps give you an idea of standards with regard to DNA testing.

  6. author paramjeet posted November 22nd 2013. 7:22 pm

    plz reply sir , if in autosomal str report the samples not matched of victim girl and accused but rape confirm. but in reality rape was committed by same accused with victims , what’s the reasons for not matching samples or autosomal str is full proof method ae nd what are the methods for matching samples. plz soon as soon possible reply I am from the victim girl

    • author dnadmin posted December 2nd 2013. 7:24 am

      Hi Paramjeet,
      Thank you for your question and my apologies for the delayed response. I’m not sure if I fully understand your question, but I’ll do my best to answer. Feel free to submit follow up questions if I missed the mark. It sounds like there is perhaps non-DNA evidence that suggests that a particular individual raped a victim, however that individual’s DNA was not detected. A couple of things come to mind: if the male had been vasectomized or had a low sperm count, it is possible that there was insufficient DNA to be detected in an autosomal STR test. Timing is also an issue. For detection of DNA from sperm, the rule of thumb is that it is difficult to detect sperm DNA more than 72 hours after coitus. If DNA from another male was detected its possible it was from a previous consensual partner. Of course, if a condom was worn during the assault sperm cells may not have been deposited. Those are just a few general considerations that I though would be helpful for readers even if I didn’t quite answer your particular inquiry.

  7. author erin jackson posted October 27th 2015. 4:14 am

    I would like to know if someone can get DNA from a digital rape kit. An if they have no DNA then how can they hold a man? An they have no other evidence tying him to the crime. Other than her statement.There witness cant even identify him.

  8. author erin jackson posted October 27th 2015. 4:17 am

    I would like to know if someone can get DNA from a digital rape kit. An if they have no DNA then how can they hold a man? An they have no other evidence tying him to the crime. Other than her statement.There witness cant even identify him. Is there any way he can get this dissmissed? They are continuing the case because the rape kit hasn’t come back yet. But Im not sure what DNA you can get from a finger?

    • author dnadmin posted October 27th 2015. 8:10 am

      Hi Erin,
      Thanks for submitting a question. Many labs can determine if even low levels of male DNA are present on rape kit swabs. Typically any DNA left behind after a male digitally penetrating a female will be relatively low in quantity. Depending on the relative amounts of male and female DNA present, the lab may need to perform more specialized type of testing. The other issue is the surrounding circumstances. For example, a brief digital penetration may leave little or no DNA. Also, the time between the alleged incident and the time of collection of the samples is a factor as to whether male DNA would be expected to be present. Along with this, the actions of the female after the alleged incident are important (was there any bathing, etc.?). The interpretation of any male DNA being present can become complicated as well. If it is extremely low, then there may be a transfer argument to explain the male DNA. I’d say in these types of cases the DNA interpretation is far from cut and dried.

  9. author Mattie Belton posted September 11th 2016. 2:16 pm

    Hello I have a question concerning Ystr testing on a partial haplotype specimen , can you explain to me what a partial haplotype means. This specimen was obtained from beneath a fingernail

    • author dnadmin posted September 11th 2016. 2:42 pm

      Hi Mattie. Haplotype refers to a DNA profile generated from the YSTR (male specific) DNA testing. Since only the Y chromosome is being considered it is a ‘haplotype’, as there is no information as to what was inherited maternally (as there would be in standard STR DNA testing). Since it is partial, there was likely an insufficient amount of male DNA to obtain DNA typing information at all loci or ‘markers’. For example, the Yfiler YSTR typing kit will give DNA information for 17 loci or markers. A partial haplotype generated with Yfiler would mean that results were obtained at less than 17 loci, so less than an optimal amount of genetic information was obtained. Hope that helps.

  10. author Rachel posted November 19th 2016. 2:50 pm


    I was just curious about DNA on a STR DNA report. A crime lab took a piece of clothing and tested it and said there was a tiny spec of blood detected, and Human DNA was isolated from 2 different individuals. How can you find out who’s blood it was if 2 different DNA’s were found.

    • author dnadmin posted November 21st 2016. 5:17 pm

      Hi Rachel,
      Great question. The testing for blood and the DNA testing are actually independent. If blood is detected and DNA from 2 individuals is detected, that does not necessarily mean that 2 people bled. Blood is rich in DNA, so if there is a major contributor to the DNA mixture it may be more likely to be from blood. Particularly with blood on clothing, you might expect a DNA mixture simply due to the wearer’s DNA being present on the clothing. So, without further information (relative percentages of DNA contribution, appearance of stain, DNA quantity, etc.) you are left with 3 likely scenarios: persons A and B in the mixture both bled, only person A bled, or only person B bled. Also, it is not possible to determine the exact number of contributors in a DNA mixture with certainty. Typically conclusions are couched in language such as ‘at least 2’, ‘at least 3’, etc.

      • author Rachel posted November 21st 2016. 6:00 pm


        Thank you for the response. As far as the blood is there a way to determine what type of blood it is? Like “normal” blood, a nose bleed or menstral blood?

        • author dnadmin posted November 21st 2016. 6:04 pm

          Not yet. There are steps being taken toward identifying menstrual blood, but I don’t believe that type of testing has yet been used in actual casework.

          • author Rachel posted November 21st 2016. 6:20 pm

            Is there a way we could have someone test what kind of blood it was, or whom would we need to talk to regarding having it tested for a specific type of blood?

          • author dnadmin posted November 21st 2016. 6:26 pm

            There is no existing available test that I know of to determine from where in the body the blood came from. I am only aware of research being conducted to differentiate menstrual blood from peripheral (other) blood.