Can forensic DNA analysis be used to generate a visual approximation of a suspect?

Can forensic DNA analysis be used to generate a visual approximation of a suspect?

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In light of the current US supreme court case, I'm curious if enough information can be teased out of a DNA sample to get a "reasonable" approximation of the suspect (never mind the legality). I realize the term reasonable is subjective, so characteristics, such as skin color, hair color/texture, approx height, eye color, freckles, etc. I came across this article a few years ago, but the company that made the test went bust in 2009. It could detect race (how accurately?). I seem to recall reading an article a few years ago stating that "soon" we'd be able to get an approximation of appearance from a DNA sample that was better than a sketch artist could provide, though I can't recall now where I read it.

In theory it's possible to have an approximation, but not to know with certainty. Identical twins have the same genomes and look very much alike. Whether it can be done in practice depends on how well we can model the relationship between genes and looks and on how much information is necessary for a judge to permit arresting and questioning a suspect.

Scientists know relatively little about how genes influence physical appearance yet. The height of the suspect is controlled by hundreds of genes with complicated interplay between them, so I don't think it's possible to estimate it just yet. Eye color is more simple: it's controlled by only 3 genes. We know weight is partially controlled by genetics but exactly which genes are responsible is not clear. Age is impossible to tell by DNA alone. Skin color should be predictable, since it's caused by melanin production, and we know which genes are responsible.

So to sum up, DNA analysis can tell the gender, skin color, and eye color of the suspect, but very little about height and weight, and virtually nothing about age. That's not enough information to identify a suspect, although perhaps someone with legal knowledge could comment on this.

But let's say in the future we know enough to determine all these traits. Then DNA analysis would be helpful but never enough to identify a suspect. The problem is that different cells in your body undergo different mutations in their DNA with time. That's how one gets cancer. Let's say there's a mutation in the eye color gene in skill cells from a murderer found on a victim's body. It won't affect the murderer's eye color but it will affect the forensic analysis. So it's impossible to know for sure what the suspect's appearance will be.

As far as I know there are ongoing efforts to find genes that affect forensically relevant traits e.g. facial characteristics and fingerprint pattern type/ridge count, and it's definitely a topic of interest to some law enforcement agencies. However as previously mentioned, there are many factors that could influence complex traits, including in utero environments and other, postnatal effects, such as nutrition, as well as the interaction between those environments and genetic influences. Given past literature showing jury-eligible members tend to over-estimate the importance and statistical accuracy of DNA profiling, however, I think even with future technological and methodological advances in genetic research, this type of evidence should be used with caution, explained with extreme care and thoroughness, and never taken as the single determining factor in reaching a verdict.

Frontiers in Genetics

The editor and reviewers' affiliations are the latest provided on their Loop research profiles and may not reflect their situation at the time of review.


Facing the unknown suspect: forensic DNA phenotyping and the oscillation between the individual and the collective

Forensic DNA phenotyping (FDP) encompasses a set of technologies geared towards inferring externally visible characteristics from DNA traces found at crime scenes. As such, they are used to generate facial renderings of unknown suspects. First, through the configuration of molecularly inscribed parts, pigmentary traits are assembled into a probabilistic rendition of the face second, facial features are landscaped from DNA to produce a metrically rendered face third, by geographically ordering DNA, an unknown suspect is attributed a particular genetic ancestry as to give him a face. We ethnographically examine these FDP practices within and beyond the laboratory to demonstrate how the promise of individuality—namely the face of the suspect—comes with the production of collectives. And it is precisely these collectives that are a matter of concern in the context of crime, as they rapidly become racialized. We show that each of these FDP practices folds in disparate histories—variously implicating the individual and the collective—while giving rise to different versions of race. The “race sorting logic” (Fullwiley in Br J Sociol 66(1):36–45, 2015) displays the tenacity of race in genetics research and its practical applications.

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Results and Discussion

Detection Limit of the Visualization Assay

The presented visualization test is especially meant for the visualization of bloodstains on dark fabrics. Therefore, undiluted bloodstains of 20 μL, 10 μL, 5 μL, and 1 μL were applied on a white (Fig. 1A) and on a dark fabric (Fig. 1C). Bloodstains on the dark fabric were invisible for the naked eye. After 30 min of incubation, bloodstains on both fabrics were made visible on the filter paper of the visualization assay (Fig. 1B and D, respectively).

Subsequently, the detection limit of the visualization assay was determined by applying 10, 2, 1, and 0.5 μL of undiluted blood and 20 μL of 1/2, 1/5, 1/10, 1/20, 1/50, 1/100, and 1/500 diluted blood on a 100% firmly woven white cotton. The visualization assay was positive for the undiluted blood spots and blood spots diluted up to 1/20. As most bloodstains on forensic evidence are undiluted and in many cases only present in very small amounts, the assay can easily be used to visualize bloodstains on dark fabrics, for example, clothes recovered from a crime scene.

Visualization and interpretation of latent bloodstains is an essential part of bloodstain pattern analysis (BPA), which is an important part of the investigation and crime scene reconstruction 22 . The bloodstain pattern remains unaffected with the presented visualization assay, which is clearly shown in Fig. 1A and B. Therefore, the visualization assay can be used to perform a BPA on a dark fabric by evaluating the transferred bloodstains on the filter paper (Fig. 1D).

Combination of the Visualization Assay with other Presumptive Blood Tests and Subsequent DNA Profiling

In a first experiment, the visualization assay was performed on a bloodstain on the fabric followed by a presumptive blood test on the same blood spot on the fabric. Although blood spots diluted more than 1/20 did not always test positive with the visualization assay, all visible blood spots on the fabric, diluted up to 1/500, tested positive for the presumptive blood tests, even if the visualization assay had been performed earlier on the same spot on the fabric. Second, a presumptive blood test was also performed on the dried transferred blood spot on the filter paper. These blood spots on the filter paper tested positive for the presumptive blood tests. Even more, bloodstains hardly visible on the white fabric and not visually detected on the filter paper (blood diluted 1/500) tested positive with the KM test which was performed on the filter paper. In real forensic cases, however, the KM test cannot be performed on invisible stains on the filter paper. Hence, we recommend spraying, for example, LumiScene on the filter paper to relocate bloodstains on the piece of evidence to be analyzed. The advantage of this technique is that no DNA degradation of the stain on the fabric will occur.

Regardless of the fact that the applied stain on the fabric was positive by the visualization assay, the stain on the fabric was subjected to DNA extraction and DNA profiling. All stains on the fabric generated a full DNA profile. Transferred bloodstains on the filter paper of undiluted blood spots and blood spots diluted 1/2, 1/5, 1/10, and 1/20 were submitted to DNA analysis. Full DNA profiles could be obtained on the filter paper of the undiluted bloodstains and bloodstains diluted 1/2. Therefore, there is no need to cut the bloodstain from the piece of fabric to obtain a DNA profile, as the transferred bloodstain on the filter paper can be used for DNA profiling. If no (full) DNA profile can be obtained from the filter paper, the stain itself should be submitted to DNA analysis.

Our data show that the visualization assay can be combined with a presumptive blood test without influencing the potential of obtaining a DNA profile from the bloodstain. The visualization assay has to be performed first as it is a simple, easy to perform, and, most importantly, inexpensive technique to visualize latent bloodstains on dark fabrics. If a positive result with the visualization assay is obtained, it should be confirmed by a presumptive blood test applied on the filter paper prior to DNA profiling. A confirmatory blood test, for example, Hexagon OBTI test, could be performed on the bloodstain to confirm whether the blood is of human or not 19 . If the visualization assay is negative, it means that either no blood is present on the fabric or that the blood is diluted more than what is visually detectable with the visualization assay. However, the most important bloodstains on the fabric useful for DNA analysis will be made visible with the presented assay. In case the visualization assay is negative, one might consider to perform a more sensitive and more expensive presumptive blood test, for example, LumiScene, on the filter paper or on the fabric. Detection of blood which is diluted more than 1/500 is interesting for forensic scientists to prove the presence of latent blood. This is especially the case when the offender tried to efface a bloodstain by thorough cleaning. However, it is less relevant for human identification by DNA profiling as these stains will theoretically not lead to useful DNA profiles.

Influence of the Type of Fabric

To investigate whether the type of fabric has an influence on the sensitivity of the visualization assay, bloodstains and blood dilutions were applied on 11 different stained and unstained fabrics of natural and (semi-)synthetic origin. Results are shown in Table 1. Undiluted blood drops of 10 μL and 2 μL on all fabric types were visually detected on the filter paper. In most cases, the visualization assay was positive for smaller drops of undiluted blood. 95.5% of 1 μL and 86.4% of 0.5 μL blood drops were visually detected on the filter paper. No clear trends were observed between different types of fabrics for undiluted blood.

Fabric 1 2 3 4 5 6 7 8 9 10 11
Type Natural Natural Natural Natural Natural Natural Synthetic Synthetic Semi-synthetic Semi-synthetic Semi-synthetic
Composition 100% cotton 100% cotton 100% cotton 100% wool 100% wool 100% leather 100% acetate 90% polyacrylamide, 10% elastane 65% polyethylene, 35% cotton 65% polyethylene, 35% cotton 80% wool, 20% nylon
Weaving Firmly Loosely Very firmly Loosely Firmly / Firmly Firmly Firmly Firmly Loosely
Garment T-shirt T-shirt Sheet Jacket collar Jacket Jacket T-shirt T-shirt T-shirt T-shirt Jumper
Color Unstained Dark gray Unstained Black Black Dark brown Dark gray Dark red Dark gray Red Dark green
Blood spot
10 μL +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+
2 μL +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+
1 μL +/+ +/+ +/+ +/+ +/− +/+ +/+ +/+ +/+ +/+ +/+
0.5 μL +/+ +/+ +/− +/− +/+ +/+ +/+ +/− +/+ +/+ +/+
20 μL 1/2 +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+ +/+
20 μL 1/5 +/+ +/+ +/+ +/+ +/+ +/+ +/− +/− +/+ +/+ +/+
20 μL 1/10 +/+ +/+ +/− +/+ +/+ +/+ +/+ +/− −/− −/− +/+
20 μL 1/20 +/+ +/+ −/− +/+ +/+ +/+ −/− −/− −/− +/− +/+
20 μL 1/50 −/− +/+ −/− +/− −/− −/− −/− −/− −/− −/− +/+
20 μL 1/100 −/− +/− −/− −/− −/− −/− −/− −/− −/− −/− +/+
20 μL 1/500 −/− −/− −/− −/− −/− −/− −/− −/− −/− −/− −/−
  • +/+ Both blood spots on the fabric tested positive.
  • +/− Only one of the two blood spots tested positive.
  • −/− Both blood spots on the fabric tested negative.

The type of fabric (synthetic, natural, or a combination of both), on which the (diluted) blood is present, has some influence on the potential to visualize it with the presented visualization assay. With the visualization assay, 20 μL of 1/2 diluted blood was visually detected on all fabrics, while 1/500 diluted blood was not visually detected on the filter paper on any of the fabrics. Blood dilutions in between those two extremes were visually detected on the filter paper as follows: 1/5: 90.9% 1/10: 72.7% 1/20: 59.1% 1/50: 22.7% and 1/100: 13.6%. Comparison of blood detection on natural fabrics and (semi-)synthetic fabrics showed slightly better results for natural fabrics. The 1/20 dilution, for example, was visually detected on the filter paper on 83.3% of the natural fabrics, visually undetectable on the synthetic fabrics, and only visually detectable on 50.0% of the semi-synthetic fabrics.

Some difference between loosely and firmly woven fabrics was observed. On loosely woven fabrics, somewhat more positive results with the visualization assay could be obtained compared to (very) firmly woven fabrics. 1/20 diluted blood was visually detected on the filter paper on all loosely woven fabrics in contrast to 35.7% of the (very) firmly woven fabrics. Moreover, 1/50 and 1/100 diluted blood were visually detected with the assay on 85.3% and 50.0% of the loosely woven fabrics, while this was impossible on the (very) firmly woven fabrics. However, on very firmly woven fabrics, a more sensitive presumptive blood test can be performed.


In the field of forensic genetics, as I elaborate below, the face and race are moving center stage. The research and the growing interest in the face contribute to what I call “the return of the phenotype”—that is, the biologization of appearances. But how does this compare with the increasing interest in the interiority of the body, in terms of genes, and with the pivotal role of genetics and genomics today? How does this compare with the commonly heard statement that race does not exist because in genetic terms humans are more than 99.9 percent the same?

When the draft of the human genome was presented to the world in June 2000, it was celebrated as a monument of humanity, and one that spoke to our commonality. This message was brought to us not through a scientific paper but by a group of powerful men gathered at the White House: Bill Clinton (president of the United States), Tony Blair (prime minister of the United Kingdom, via a conference call), Francis Collins (director of the National Human Genome Research Institute), and Craig Venter (chief executive of Celera Genomics). We are, Clinton told us, more “than 99.9 percent the same.” 5 5 See:
However, the genetic research that was sparked by this important achievement in life science research, the map of the human genome, turned out to be centered not so much on our sameness but rather on that 0.1 percent of difference. The focus on difference as a site to learn about genetic diseases, genetic genealogy, or forensic genetics turned out to be much more promising.

Large databases have been developed since then through the International Haplotype Mapping Project, the 1000 Genomes Project, and, more recently, the All of Us project, among others. 6 6 See:
This focus on difference has itself attracted attention and critique, and thus has become equally present in social science research on genetics and genomics. An important and influential observation in this scholarship is that despite the promise of the common genome, race did not become irrelevant in life science research. Although genetics and genomic research claim to be colorblind or “postracial,” various scholars argue that such research is contributing to the “reinscription of race at the molecular level” (Duster 2006 , 428 see also Abu El-Haj 2007 Fullwiley 2007 Skinner 2006 ).

Although this process of molecularizing difference is highly important and requires ongoing attention in the context of big data and data-mining endeavors, here I want to suggest that in the life sciences we are increasingly witnessing the return of the phenotype—in other words, the biologization of appearance. The growing interest in the biology of appearance is reconfiguring relations between the individual and the population as well as shaping what race is made to be. The return of the phenotype might lead to the suggestion that genes map neatly onto appearance and, the other way around, that appearance can predict a person's genetic composition or even behavior. It is precisely this assumed causal relation between genotype and phenotype that I problematize. Moreover, with the return of the phenotype, I suggest that race is becoming a matter of sur-face. 7 7 I obviously play with face and surface, but the much more substantial point concerns the history of physical anthropology, where the study of human variation was much more about the surface of the body and its environment.
Might it then be that Ashley Montagu's observation—that while physical anthropologists were clinging to the race concept, geneticists had moved beyond it (Visweswaran 1998 , 74)—is currently being overturned with an increasing interest in the phenotype? Might this interest in the phenotype risk introducing racial typologies through the front door?

Y-chromosome short tandem repeats in forensics—Sexing, profiling, and matching male DNA

Department of Forensic Genetics, Institute of Legal Medicine and Forensic Sciences, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin and Berlin Institute of Health, Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany

Lutz Roewer, Department of Forensic Genetics, Institute of Legal Medicine and Forensic Sciences, Charité-Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany.

Department of Forensic Genetics, Institute of Legal Medicine and Forensic Sciences, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin and Berlin Institute of Health, Charité-Universitätsmedizin Berlin, 13353 Berlin, Germany

Lutz Roewer, Department of Forensic Genetics, Institute of Legal Medicine and Forensic Sciences, Charité-Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany.


The analysis of short tandem repeat (STR) markers located on the Y chromosome is an established method in forensic casework analysis. Usually this method is applied in cases of male-on-female sexual assault, in which the victim's DNA is in great excess and masked the male contribution. Y-STR analysis is able to detect the presence of minuscule amounts of male DNA of one or multiple donors and resulting genetic profiles can be compared to known reference samples. The expert has to determine whether the Y-STR result of a trace is suitable for a biostatistical calculation in case of a match. The Discrete Laplace method which is implemented in the Y chromosome haplotype reference database (YHRD) can be used to estimate haplotype frequencies with a better approximation than other methods namely the counting method. Moreover, Y-SNPs in combination with Y-STRs can infer the biogeographical origin of an unknown male person with comparably high precision due to the availability of a robust phylogenetic tree and large reference data collections. Y-based ancestry prediction and familial searching can, therefore, provide important investigative leads in crime cases without suspect.

  • Forensic Biology > Haploid Markers
  • Forensic Biology > Ancestry Determination using DNA Methods
  • Forensic Biology > DNA Databases and Biometrics
  • Forensic Biology > Forensic DNA Technologies


STR markers located on the Y chromosome and the Y Chromosome Haplotype Reference Database (YHRD) are used to analyze and interpret DNA evidence in sexual assault investigations.

10 Cool Technologies Used in Forensic Science

1. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) : When broken glass is involved in a crime, putting together even tiny pieces can be key to finding important clues like the direction of bullets, the force of impact or the type of weapon used in a crime. Through its highly sensitive isotopic recognition ability, the LA-ICP-MS machine breaks glass samples of almost any size down to their atomic structure. Then, forensic scientists are able to match even the smallest shard of glass found on clothing to a glass sample from a crime scene. In order to work with this type of equipment in conjunction with forensic investigation, a Bachelor’s Degree in Forensic Science is usually necessary.

2. Alternative Light Photography : For a forensic nurse, being able to quickly ascertain how much physical damage a patient has suffered can be the difference between life and death. Although they have many tools at their disposal to help make these calls quickly and accurately, Alternative Light Photography is one of the coolest tools to help see damage even before it is visible on the skin. A camera such as the Omnichrome uses blue light and orange filters to clearly show bruising below the skin’s surface. In order to use this equipment, you would need a MSN in Forensic Nursing.

3. High-Speed Ballistics Photography : You might not think of it right away as a tool for forensic scientists, but ballistics specialists often use high-speed cameras in order to understand how bullet holes, gunshot wounds and glass shatters are created. Virtually anyone, from a crime scene investigator to a firearms examiner, can operate a high-speed camera without any additional education or training. Being able to identify and match bullet trajectories, impact marks and exit wounds must be done by someone with at least a Bachelor’s of Science in Forensic Science.

4. Video Spectral Comparator 2000 : For crime scene investigators and forensic scientists, this is one of the most valuable forensic technologies available anywhere. With this machine, scientists and investigators can look at a piece of paper and see obscured or hidden writing, determine quality of paper and origin and “lift” indented writing. It is sometimes possible to complete these analyses even after a piece of paper has been so damaged by water or fire that it looks unintelligible to the naked eye. In order to run this equipment, at least a Bachelors degree in Forensic Science or a Master’s Degree in Document Analysis is usually required.

5. Digital Surveillance For Xbox (XFT Device) : Most people don’t consider a gaming system a potential place for hiding illicit data, which is why criminals have come to use them so much. In one of the most ground-breaking forensic technologies for digital forensic specialists, the XFT is being developed to allow authorities visual access to hidden files on the Xbox hard drive. The XFT is also set up to record access sessions to be replayed in real time during court hearings. In order to be able to access and interpret this device, a Bachelor’s Degree in Computer Forensics is necessary.

6. 3D Forensic Facial Reconstruction : Although this forensic technology is not considered the most reliable, it is definitely one of the most interesting available to forensic pathologists, forensic anthropologists and forensic scientists. In this technique, 3D facial reconstruction software takes a real-life human remains and extrapolates a possible physical appearance. In order to run this type of program, you should have a Bachelor’s Degree in Forensic Science, a Master’s Degree in Forensic Anthropology or a Medical Degree with an emphasis on Forensic Examination and Pathology.

7. DNA Sequencer : Most people are familiar with the importance of DNA testing in the forensic science lab. Still, most people don’t know exactly what DNA sequencers are and how they may be used. Most forensic scientists and crime lab technicians use what’s called DNA profiling to identify criminals and victims using trace evidence like hair or skin samples. In cases where those samples are highly degraded, however, they often turn to the more powerful DNA sequencer, which allows them to analyze old bones or teeth to determine the specific ordering of a person’s DNA nucleobases, and generate a “read” or a unique DNA pattern that can help identify that person as a possible suspect or criminal.

8. Forensic Carbon-14 Dating : Carbon dating has long been used to identify the age of unknown remains for anthropological and archaeological findings. Since the amount of radiocarbon (which is calculated in a Carbon-14 dating) has increased and decreased to distinct levels over the past 50 years, it is now possible to use this technique to identify forensic remains using this same tool. The only people in the forensic science field that have ready access to Carbon-14 Dating equipment are forensic scientists, usually with a Master’s Degree in Forensic Anthropology or Forensic Archaeology.

9. Magnetic Fingerprinting and Automated Fingerprint Identification (AFIS) : With these forensic technologies, crime scene investigators, forensic scientists and police officers can quickly and easily compare a fingerprint at a crime scene with an extensive virtual database. In addition, the incorporation of magnetic fingerprinting dust and no-touch wanding allows investigators to get a perfect impression of fingerprints at a crime scene without contamination. While using AFIS requires only an Associates Degree in Law Enforcement, magnetic fingerprinting usually requires a Bachelor’s Degree in Forensic Science or Crime Scene Investigation.

10. Link Analysis Software for Forensic Accountants : When a forensic accountant is trying to track illicit funds through a sea of paperwork, link analysis software is an invaluable tool to help highlight strange financial activity. This software combines observations of unusual digital financial transactions, customer profiling and statistics to generate probabilities of illegal behavior. In order to accurately understand and interpret findings with this forensic technology, a Master’s Degree in Forensic Accounting is necessary.

Appendix 6A

The following tables summarize the law in the United States on the admissibility of estimates of profile frequencies or random-match probabilities of DNA types. Table 6.1 lists the leading cases or statutes in each jurisdiction with a parenthetical explanation of the result in each case. Table 6.2 presents this information in a more abbreviated format. In many of the more recent cases, both an interim-ceiling and product-rule estimates were presented. The tables do not show whether an opinion holds or suggests that the product-rule estimate would have been inadmissible had the ceiling estimate not been included. Many other subtleties and issues that arise in these cases are not captured in this brief summary.


Leading Cases and Statutes on Admissibility of Inclusionary DNA Evidence by Jurisdiction, as of June 1995.


Use evidence found in DNA fingerprint patterns to argue which suspect committed a crime.

PE: HS-LS3-2
Time Requirement: 2 45-minute Class Periods

SEP: Engaging in argument from evidence
CCC: Cause and Effect
DCI: LS3.B: Variation of Traits

Intermediate �sy to perform requires some background knowledge.

  • Introduce students to the use of DNA analysis in forensic investigations
  • Perform a technically simple, hands-on experiment in 45 minutes with 9-V batteries
  • Discuss advanced topics of PCR and DNA fingerprinting

Solve a forensic mystery using the tools of biotechnology and the concept of DNA fingerprinting. Students cast agarose gels, load predigested DNA samples, and perform electrophoresis with one to three 9-V batteries. They stain the gels and analyze the banding patterns of DNA collected from the suspects and the crime scene. Demo kit includes beautifully illustrated instructions, free 1-year access to digital resources that support 3-dimensional instruction, as well as needed materials and equipment for 1 instructor to perform the demonstration twice to a classroom. Materials are durable and reusable with replacement parts available.

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Hands-on Activity DNA Profiling & CODIS: Who Robbed the Bank?

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  • Biomedical Engineering and the Human Body
    • Engineering Bones
      • Prosthetic Party: Build and Test Replacement Legs
      • Sticks and Stones Will Break That Bone!
      • Muscles, Oh My!
        • The Artificial Bicep
        • Measuring Our Muscles
        • Body Circulation
          • Clearing a Path to the Heart
          • Breathe In, Breathe Out
            • Polluted Air = Polluted Lungs
            • Digestion Simulation
              • Protect That Pill
              • My Mechanical Ear Can Hear!
                • Sounds All Around
                • Biomedical Devices for the Eyes
                  • Protect Those Eyes
                  • We've Come a Long Way, Baby!
                    • You're the Expert
                    • DNA: The Human Body Recipe
                      • DNA Profiling & CODIS: Who Robbed the Bank?
                      • DNA Build
                      • Bone Fractures and Engineering
                        • Repairing Broken Bones
                        • Living with Your Liver

                        TE Newsletter

                        Students examine DNA to determine who robbed the bank


                        Engineering Connection

                        Biomedical engineers who understand the science of genetics create tools, equipment and processes to accurately collect and examine DNA evidence for crime and paternity cases. These engineers also work with attorneys and in court systems to explain how DNA profiling works.

                        Learning Objectives

                        After this activity, students should be able to:

                        • Describe the organization of DNA into repeating nucleotide base pair sequences
                        • Explain how DNA profiling is used to link people to crime and paternity cases.
                        • Describe the role of biomedical engineering in DNA profiling.

                        Educational Standards

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                        NGSS: Next Generation Science Standards - Science
                        • Conduct an investigation to produce data to serve as the basis for evidence that meet the goals of an investigation. (Grades 6 - 8) More Details

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                        • Use mathematical representations to describe and/or support scientific conclusions and design solutions. (Grades 6 - 8) More Details

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                        • Advances in technology influence the progress of science and science has influenced advances in technology. (Grades 6 - 8) More Details

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                        Common Core State Standards - Math
                        • Understand that statistics can be used to gain information about a population by examining a sample of the population generalizations about a population from a sample are valid only if the sample is representative of that population. Understand that random sampling tends to produce representative samples and support valid inferences. (Grade 7) More Details

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                        • Students will develop an understanding of the relationships among technologies and the connections between technology and other fields of study. (Grades K - 12) More Details

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                        • Use direct and indirect observations, evidence, and data to support claims about genetic reproduction and traits of individuals (Grade 8) More Details

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                        Materials List

                        Worksheets and Attachments

                        More Curriculum Like This

                        As a class, students work through an example showing how DNA provides the "recipe" for making human body proteins. They see how the pattern of nucleotide bases (adenine, thymine, guanine, cytosine) forms the double helix ladder shape of DNA, and serves as the code for the steps required to make gene.

                        Students reinforce their knowledge that DNA is the genetic material for all living things by modeling it using toothpicks and gumdrops that represent the four biochemicals (adenine, thiamine, guanine, and cytosine) that pair with each other in a specific pattern, making a double helix. Student teams.

                        Students learn about mutations to both DNA and chromosomes, and uncontrolled changes to the genetic code. They are introduced to small-scale mutations (substitutions, deletions and insertions) and large-scale mutations (deletion duplications, inversions, insertions, translocations and nondisjunction.

                        In a class discussion format, students are presented with background information about basic human genetics.The number of chromosomes in both body cells and egg and sperm cells is covered, as well as the concept of dominant and recessive alleles.

                        Pre-Req Knowledge

                        Familiarity with DNA and its constituent nucleotide base pairs.


                        A robbery takes place at a bank. As the thief escapes the building, a security guard grabs one of the bank robber's gloves. The bank robber leaves the scene in a phone service van. The phone company identifies three employees who may have been in the vicinity of the bank at the time of the robbery. All employees deny robbing the bank. Can you think of some way, besides witness testimony, that the bank robber could be identified from among the three individuals?

                        DNA evidence is more reliable than fingerprints at identifying people.

                        DNA can identify people — even better than fingerprints. DNA is found in all of our cells: hair, teeth, bones, blood and skin. Though all humans share 99.9% of their genes, our DNA differs from everyone else's by three million nucleotide base pairs.

                        Our DNA is organized in 23 chromosomes in the nucleus in each of our cells. Regions in each chromosome contain what are called "junk DNA," which does not contain genes. But often, this junk DNA contains repeating nucleotide base pair sequences that can be used for matching purposes. (Show students Figure 1 or the same image in the attached CODIS Visual Aid.) In this example, you can see chromosome locations where the FBI looks for repeating sequences of DNA. They're called CODIS sites, which stands for the FBI's Combined DNA Index System.

                        Figure 1. The 23 human chromosomes and 13 chromosomal locations at which the FBI looks for repeating DNA sequences. For this activity, note the TPOX region on chromosome 2. (X and Y count as one chromosome pair. The AMELs are not CODIS sites.)

                        In our case, the police found a hair in the bank robber's glove. Remember that we have 23 pairs of chromosomes, each pair containing one chromosome from our father, the other from our mother. A DNA analysis shows that the hair in the robber's glove contains the following nucleotide base pair sequences in the TPOX region (show students Figure 2 or the same image in the attached CODIS Visual Aid).

                        Figure 2. TPOX region of chromosome 2 of hair found in bank robber's glove.

                        Note that the GAAT sequence is repeated twice in the father's side and three times in the mother's side (the sides of each chromosome are often not the same length). Equivalently, we could say that the CTTA sequence is repeated. Why is that? (G always pairs with C, and A always pairs with T).

                        So now let's compare the TPOX regions of the DNA found in the bank robber's glove with the TPOX regions of the DNA of two suspects. Note that we are just looking at the one side of the DNA with the GAAT repeating sequence. This simplifies the comparison. (Show students Figure 3 or the same image in the attached CODIS Visual Aid.)

                        Figure 3. Comparison of the TPOX region of Chromosome 2 of the unknown bank robber and two suspects.

                        Suspect 1 matches the GAATGAAT sequence of the hair found in the glove on one chromosome, but the other chromosome does not match. Both chromosomes must match to show that the hair in the glove came from a specific suspect. Thus, from just one CODIS site we already know that the hair in the bank robber's glove cannot belong to suspect 1.

                        Suspect 2 matches the GAATGAAT sequence on one chromosome and the GAATGAATGAAT sequence on the other chromosome, so you can say that suspect 2 matches at the TPOX location. To confirm that the hair belongs to suspect 2, the other 12 chromosome locations (see Figure 1) must also match. If all 13 CODIS locations match, then the hair in the bank robber's glove belongs to suspect 2.

                        The random probability that one of your CODIS sites matches with someone else's is about one in 10 (1/10). Therefore, the probability of two CODIS sites matching is 1/10*1/10 = 1/100 (one in 100). The chance of three CODIS sites matching randomly is 1/10*1/10*1/10 = (1/10) 3 = 1/1000 (one in 1,000). The random chance that all 13 CODIS sites match is (1/10) 13 = one in 10,000,000,000,000. The chance of being struck by lightning in your lifetime is, roughly, one in 1,000,000. So you are 10 million times more likely to be struck by lightning than you are to have the same 13 CODIS sequences as another person. This is what makes DNA profiling so certain.

                        Engineers can be involved in many aspects of crime scene investigation. They might use their knowledge of CAD (computer-aided drawing) to create a reconstruction of the crime scene. First they might develop a model of the room, and then determine the path of bullets and analyze the blood splatter patterns to determine the position of victims and their killers at the time of the crime. Biomedical engineers create the tools, equipment and processes to accurately collect and examine DNA evidence for crime and paternity cases. Biomedical engineers also help investigators with the analysis of the gene sequencing for DNA profiling.


                        In this activity, probability is used to determine which suspect is the most likely match. We are told that the likelihood of a random match between a CODIS site for one person and someone else is 1/10. Why is that? Each of the regions that we are considering here contains an allele, or, a version of a gene. Which allele you have at a particular site is determined by your parents' genetic data and meiosis, as well as any errors in replication. However, these alleles are not unique in a population you can have the same allele as someone else. Statisticians study populations to get an idea about the distribution of alleles (how many people have each kind of allele). In this way, statisticians can estimate a probability that any two people have the same allele. If the likelihood of a CODIS site match between two random people was much greater or much less than the 1/10 used in this activity, the number of matches we would need in order to be reasonably certain of the suspect's guilt would also change.

                        • Make copies of the Suspect CODIS Analysis Worksheet, one per team.
                        • Set the stage for the activity by conducting the Introduction/Motivation section.
                        1. Divide the class into pairs of students, and pass out a worksheet to each team.
                        2. Assist students as they complete their worksheets.
                        3. Have teams conclude by writing on their worksheets which suspect their DNA profiling implicates in the robbery.
                        4. Have the teams with the correct answer describe how they arrived at their conclusion. (Answer: Suspect 2 seems likely based on a match with four CODIS sites).
                        5. Have students calculate the likelihood that suspect 2, even though he matches four CODIS sites, is not the owner of the hair in the bank robber's glove. (Answer: (1/10) 4 = 1 in 10,000, not good enough – need more CODIS site data)
                        6. Have students act as biomedical engineers and analyze the results of the DNA profiling for the police investigators as described in the post-assessment activity.


                        base pair: Two nucleotide bases that form a "rung of the DNA ladder." A DNA nucleotide is made of a molecule of sugar, a molecule of phosphoric acid, and a molecule called a base. The bases are the "letters" that spell out the genetic code. In DNA, the code letters are A, T, G and C, which stand for the chemicals adenine, thymine, guanine and cytosine, respectively. In base pairing, adenine always pairs with thymine, and guanine always pairs with cytosine.

                        biomedical engineer: A person who blends traditional engineering techniques with the biological sciences and medicine to improve the quality of human health and life. Biomedical engineers design artificial body parts, medical devices, diagnostic tools, and medical treatment methods.

                        chromosome: One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes plus two sex chromosomes. Each parent contributes one chromosome to each pair, so children receive half of their chromosomes from their mothers and half from their fathers.

                        CODIS: Acronym for the FBI's DNA identification system: Combined DNA Index System. See:

                        CODIS sites: The 13 regions of the chromosomes at which the FBI CODIS looks for repeating DNA sequences for matching purposes.

                        DNA: Deoxyribonucleic acid contains the genetic instructions that control the biological development of our cells and the proteins the cells make. DNA codes the sequence of the amino acids in proteins using the genetic code, a triplet code of nucleotide bases.

                        DNA fingerprinting: A method for identifying individuals by the particular structure of their DNA. Because the structure of each person's DNA is different, just like our fingerprints, we can be identified from our DNA. This technique became known to the public as "DNA fingerprinting" because of its powerful ability to discriminate between unrelated individuals.

                        DNA profile: The result of determining the relative positions of DNA sequences at several locations on the molecule. Each person (except identical twins) has a unique DNA profile when used in the context of the CODIS database, which evaluates 13 specific DNA locations.

                        engineer: A person who applies his/her understanding of science and math to creating things for the benefit of humanity and our world.

                        gene: Segments of DNA that get translated into proteins.

                        junk DNA: Stretches of DNA that do not code for genes "most of the genome consists of junk DNA." Junk DNA contains repeating base pair sequences that can be used for matching purposes.

                        nucleotide bases: The parts of RNA and DNA involved in pairing they include cytosine, guanine, adenine, thymine (DNA) and uracil (RNA), abbreviated as C, G, A, T and U. They are usually simply called bases in genetics. Also called base pairs.


                        Discussion/Brainstorming: As a class, ask students if they can think of some way that a bank robber could be identified if no one saw who he or she was. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Brainstorming is how engineers come up with creative ideas. Have them raise their hands to respond. Record their ideas on the board.

                        Activity Embedded Assessment

                        Worksheet: Have students complete the activity worksheet review their answers to gauge their mastery of the subject.

                        Engineering Analysis: Have students act as biomedical engineers and analyze the results of the DNA profiling for the police investigators. Have each team state which suspect their DNA profiling implicates in the crime. How certain are their results? Next, have the students write a brief one-page report on their results that they might deliver to the police investigators. In this report, they should explain the outcomes of the DNA profiling, how they arrived at their results, and how they determined the certainty of their results.

                        Safety Issues

                        Troubleshooting Tips

                        If students have difficulty, work through the first CODIS site on the worksheet with them.

                        Sometimes it helps to cut out the robbery evidence CODIS data columns from the worksheet and hold them right next to the suspect data columns, making it easier to compare for matches of repeating base pair sequences.

                        Activity Extensions

                        Have students conduct the online, animated Catch a Criminal activity that includes a real-world 13 CODIS site analysis using three suspects. See the Koshland Science Museum's Putting DNA to Work website:

                        With the popularity of the CSI television shows, students may have some understanding of forensic evidence. Along these lines, have students investigate the creative tools, equipment and processes used to accurately collect and examine DNA evidence for crime, paternity and ancestry investigations.