DNA Technologies, Screening, Fingerprints and Sequencing
In 2023, Australian police solved a 1984 cold case using DNA genealogy databases, 39 years after the crime, one person in 10 billion matched.
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Q1 · What do you already know about how DNA is used to solve crimes or identify people?
Think about TV shows, news stories or real cases where DNA evidence played a role.
Q2 · If your DNA was stored in a police database, what are some potential benefits and risks you can think of?
Consider both the power of DNA to solve crimes and the privacy concerns about storing genetic information.
● Know
- That DNA profiling creates a unique genetic fingerprint
- The basic concept of gel electrophoresis as a separation technique
- That DNA sequencing reads the order of bases in DNA
● Understand
- How DNA profiling can be used to identify individuals and relationships
- Why DNA evidence is powerful but not infallible
- The difference between DNA profiling and DNA sequencing
● Can do
- Interpret a simple DNA profile pattern conceptually
- Explain applications of DNA technologies in Australian contexts
- Evaluate the strengths and limitations of DNA evidence
A forensic scientist swabs a crime scene and recovers just a few nanograms of DNA, far too little to test. Within hours, a machine amplifies that trace into billions of copies ready for analysis. PCR (Polymerase Chain Reaction) is the method that makes this possible, copying a specific segment of DNA millions of times. It is so sensitive that it can work from a single hair, a drop of saliva or a tiny bloodstain. Without PCR, forensic analysis and ancient DNA research would be impossible because most samples contain far too little DNA to analyse directly.
Gel electrophoresis separates DNA fragments by length. DNA is negatively charged, so it moves through a gel toward the positive electrode. Smaller fragments move faster and farther, creating distinct bands. DNA sequencing reads the exact order of bases, and DNA profiling compares short repeating sequences that vary greatly between individuals, the basis of forensic identification and paternity testing.
In 1984, British geneticist Alec Jeffreys developed DNA profiling by accident while studying how genes evolve. The first forensic use came in 1987, when it cleared a suspect in a double murder and helped convict the real killer. Since then, DNA evidence has exonerated hundreds of wrongly convicted people worldwide, including several in Australia.
Australian forensics: The Australian Federal Police and state forensic laboratories use DNA profiling to solve crimes and identify disaster victims. The National Criminal Investigation DNA Database (NCIDD) allows cross-jurisdictional matching of profiles, while strict privacy laws govern whose DNA can be stored and for how long.
Tap each card to flip. Mark Got it when you can recall the answer without flipping.
DNA technology has transformed fields far beyond forensics. In medicine, genetic screening can identify carriers of recessive disorders, predict responses to drugs, and diagnose inherited diseases before symptoms appear. Newborns in Australia are screened for conditions like phenylketonuria (PKU) using a simple blood spot test, allowing dietary intervention that prevents intellectual disability.
In ancestry research, DNA testing can trace geographic origins and identify biological relatives. In conservation, genetic analysis helps track endangered populations, detect illegal wildlife trade and design breeding programs. The information is powerful, but so are the ethical obligations. Who owns your genetic data? Can insurers or employers demand access? These questions are still being debated by lawmakers around the world.
The Human Genome Project, completed in 2003, sequenced the entire human genome, about 3 billion base pairs, for the first time. It cost roughly US$2.7 billion and took 13 years. Today, a complete human genome can be sequenced for under US$1,000 in a single day. This collapse in cost has democratised genetics, enabling research and clinical applications that were unimaginable two decades ago.
Australian health: The Garvan Institute's Kinghorn Centre for Clinical Genomics in Sydney is one of the world's largest genome sequencing facilities. It sequences thousands of Australian genomes annually to diagnose rare diseases, guide cancer treatment and contribute to global genetic databases that improve care for everyone.
A police lab receives a blood sample from a crime scene and a cheek swab from a suspect. The DNA profiles from the two samples match at 15 out of 20 markers, but differ at 5 markers. Should the suspect be charged?
In standard DNA profiling, a match at even one mismatching marker usually rules out a suspect. The 5 mismatches mean the blood almost certainly did not come from this suspect. However, the partial match suggests the true donor may be a close relative, because siblings and parents share about 50% of their DNA markers.
Use these terms in your explanation: marker · profile · relative · exclusion
One of the most exciting frontiers in DNA technology is personalised medicinetailoring treatments to an individual's genetic makeup. Pharmacogenomics studies how genes affect drug responses. Some people metabolise certain drugs too quickly, making them ineffective; others metabolise too slowly, leading to dangerous side effects. Genetic testing can predict these responses before a drug is prescribed.
Ancient DNA analysis is another revolution. By extracting and sequencing DNA from bones, teeth and sediment thousands of years old, scientists can reconstruct the genomes of extinct species and ancient human populations. This has revealed interbreeding between modern humans and Neanderthals, traced the spread of agriculture across Europe, and identified the bacterium responsible for the Black Death.
The breast cancer genes BRCA1 and BRCA2 were identified through genetic linkage studies. Women with harmful mutations in these genes have a 60-70% lifetime risk of developing breast cancer and a elevated risk of ovarian cancer. Genetic screening allows carriers to choose enhanced surveillance or preventive surgery, dramatically reducing their risk.
Australian ancient DNA: Researchers at the University of Adelaide and the Australian Centre for Ancient DNA (ACAD) extract DNA from Aboriginal Australian remains and Tasmanian devil fossils. Their work has revealed deep-time connections between Indigenous Australians and the first people to leave Africa, and is helping to understand how Tasmanian devils lost genetic diversity before the arrival of Europeans.
DNA technologies have transformed criminal justice, family law, medicine and our understanding of human history. Here are the major applications you need to know.
Forensics
DNA profiling is one of the most powerful tools in criminal investigations. A single hair, drop of blood or skin cell left at a crime scene can be enough to identify a suspect or exonerate an innocent person. Since 1989, DNA evidence has been used to overturn hundreds of wrongful convictions in the United States alone, including some death row cases. In Australia, forensic DNA analysis is conducted by state police laboratories and the Australian Federal Police (AFP).
Paternity and Relationship Testing
A child inherits half their DNA from their mother and half from their father. By comparing STR profiles, scientists can determine with near-certainty whether a man is the biological father of a child. DNA testing can also confirm sibling relationships, identify remains after disasters and reunite separated families.
Ancestry and Population Genetics
Commercial DNA testing services analyse your DNA and compare it to reference databases from populations around the world. This can reveal your genetic ancestry, migratory history and even distant relatives. From a scientific perspective, these databases also help researchers study human migration patterns and genetic diversity.
Medical Screening and Personalised Medicine
DNA sequencing can identify mutations that cause or increase the risk of genetic diseases such as cystic fibrosis, Huntington's disease and certain types of cancer. In Australia, newborn screening programs test babies for treatable genetic conditions. As sequencing becomes cheaper, personalised medicinetailoring treatments to a person's genetic makeup, is becoming a reality.
The NSW Forensic DNA Database is one of Australia's most important criminal justice tools. Under the Forensic Procedures Act 2000 (NSW), police can collect DNA samples from suspects and convicted offenders. These profiles are stored in a database and can be matched against DNA from crime scenes. The database has solved thousands of cases, including cold cases decades old. However, it also raises privacy concerns: your DNA contains information about your health, ancestry and relatives. In 2023, Australian researchers at the Garvan Institute of Medical Research in Sydney sequenced the genomes of thousands of Australians as part of the Genomics Health Futures Mission, aiming to improve diagnosis and treatment of rare diseases and cancer.
DNA Profile Interpretation
1 The crime scene DNA and suspect DNA show identical band patterns. What does this suggest? Why is this not absolute proof on its own?
2 Why do forensic scientists examine 13-20 different STR locations rather than just one?
3 Explain why identical twins cannot be distinguished by standard DNA profiling.
DNA Technology in Society
1 A police DNA database stores genetic profiles of convicted criminals. Some civil liberties groups argue this violates privacy. Provide one argument FOR and one argument AGAINST storing DNA in a police database.
2 Distinguish between DNA profiling and DNA sequencing. Give one application where each is most appropriate.
3 The Garvan Institute in Sydney is sequencing Australian genomes to improve cancer treatment. Explain how knowing a patient's exact DNA sequence could lead to better medical outcomes than standard treatment.
Copy Into Your Book
▼Core Definitions
- DNA profiling = unique genetic fingerprint using STRs
- Gel electrophoresis = separates DNA by size
- DNA sequencing = reads the order of A, T, G, C
- STR = short tandem repeat; highly variable
How Profiling Works
- Collect DNA sample
- Amplify STR regions
- Separate by gel electrophoresis
- Compare band patterns
Applications
- Forensics, crime scene matching
- Paternity, family relationships
- Ancestry, genetic origins
- Medicine, disease risk, personalised treatment
Australian Context
- NSW Forensic DNA Database
- AFP forensic laboratories
- Garvan Institute genome research
- Genomics Health Futures Mission
At the start of this lesson you were told that Australian police used DNA genealogy databases to identify a suspect in a 1984 cold case, 39 years after the crime, using a DNA fingerprint unique to roughly one person in 10 billion. That story was designed to show you how precise and powerful DNA technologies have become.
Now that you understand how DNA profiling, sequencing and screening actually work, explain how that cold-case identification would have been possible. What aspect of these technologies surprised you most, and how does your new understanding change the way you think about DNA evidence?
Q1. Explain what DNA profiling is and why it uses short tandem repeats (STRs) rather than sequencing the entire genome. 3 MARKS
Q2. Describe the process of gel electrophoresis conceptually and explain how it is used in DNA profiling. 4 MARKS
Q3. Distinguish between DNA profiling and DNA sequencing . For each, identify one application where it is the most appropriate technology and justify your choice. 5 MARKS
Revisit Your Initial Thinking
Go back to your Think First responses at the top of the lesson.
- Did you correctly identify that DNA profiling compares specific variable regions, not whole genomes?
- Did you consider both the power and the privacy risks of DNA identification?
- Write one sentence summarising the most important thing you learned about how DNA technologies serve society.
Model answers (click to reveal)
Comprehensive Answers
▼Activity 1, DNA Profile Interpretation
1. Identical band patterns: Identical patterns strongly suggest the crime scene DNA came from the suspect [1 mark]. However, this is not absolute proof because DNA evidence must be considered alongside other evidence (motive, opportunity, alibi), and contamination or mishandling of samples is possible [1 mark].
2. Multiple STR locations: Examining many locations dramatically reduces the chance of a random match [1 mark]. While one location might match by coincidence, the probability of matching at 20 independent locations is less than one in a billion [1 mark].
3. Identical twins: Identical twins develop from the same fertilised egg and therefore share virtually identical DNA [1 mark]. Standard DNA profiling cannot distinguish them because it examines the same DNA regions [1 mark].
Activity 2, DNA Technology in Society
1. Police database arguments: FOR: DNA databases have solved thousands of crimes, including cold cases, and can exonerate innocent people [1 mark]. AGAINST: DNA contains sensitive health and ancestry information; storing it indefinitely raises concerns about surveillance, data breaches and potential misuse by governments or hackers [1 mark].
2. Profiling vs sequencing: DNA profiling analyses specific variable regions (STRs) to create a unique pattern for identification [1 mark]. Best for forensics and paternity testing because it is fast, cheap and highly discriminating [1 mark]. DNA sequencing reads the exact order of all bases in a DNA segment [1 mark]. Best for medical diagnosis and research because it can reveal mutations and disease-causing changes [1 mark].
3. Genome sequencing for cancer: Knowing a patient's exact DNA sequence can reveal specific mutations driving their cancer [1 mark]. This allows doctors to choose targeted therapies that attack those specific mutations [1 mark]. It also helps predict how a patient will respond to different drugs, avoiding treatments that are unlikely to work and reducing side effects [1 mark].
Multiple Choice
1. BDNA profiling analyses STRs, not the whole genome. Option A describes genome sequencing. Option C is too narrow. Option D is incorrect, while mitochondrial DNA can be used, standard profiling uses nuclear STRs.
2. CSmaller fragments move more easily through gel pores. Option A is wrong, DNA is negatively charged. Option B is backwards, smaller fragments are lighter, not heavier. Option D is incorrect, dye absorption does not affect movement.
3. AA match at 20 STR locations makes it extremely likely the DNA came from the same person. Option B overstates the case, guilt requires more than DNA. Option C confuses DNA presence with timing. Option D contradicts established science.
4. DSequencing reads exact base orders and can find mutations. Option A is wrong, profiling does not read sequences. Option B is wrong, gel electrophoresis only separates by size, it does not identify mutations. Option C is irrelevant.
5. BDNA contains health, ancestry and relative information beyond criminal identity. Option A is false, profiles are unique. Option C is an unsupported generalisation. Option D is false, DNA does not change significantly over a person's lifetime.
Short Answer Model Answers
Q6 (3 marks): DNA profiling is a technique that analyses specific variable regions of DNA to create a unique pattern that can identify an individual [1 mark]. It uses STRs because these short tandem repeats vary greatly between individuals, making them excellent genetic markers [1 mark]. Sequencing the entire genome would be unnecessary, far more expensive and much slower for identification purposes [1 mark].
Q7 (4 marks): Gel electrophoresis separates DNA fragments by size using an electric field and a gel matrix [1 mark]. DNA is loaded into wells at one end of the gel, and an electric current pulls the negatively charged DNA toward the positive electrode [1 mark]. Smaller fragments travel further through the gel pores than larger fragments [1 mark]. In DNA profiling, this technique is used to separate amplified STR fragments so that the band pattern, which is unique to each individual, can be visualised and compared between samples [1 mark].
Q8 (5 marks): DNA profiling analyses specific highly variable regions (STRs) to produce a unique genetic fingerprint for identification [1 mark]. It is most appropriate for forensic investigations because it is fast, relatively inexpensive and can match crime scene DNA to suspects with extremely high confidence [1 mark]. DNA sequencing determines the exact order of nucleotide bases in a DNA molecule [1 mark]. It is most appropriate for medical diagnosis because it can identify specific mutations that cause or increase the risk of genetic diseases, enabling personalised treatment plans [1 mark]. Profiling tells you who; sequencing tells you what is in the DNA [1 mark].
Jump Through Genetics!
Climb platforms using your knowledge of DNA technologies, forensics and genome sequencing. Pool: Lesson 8.