DNA mod lec 2

What does “rubbish in, rubbish out” mean in forensic DNA?

If the sample or data handling is poor, the results will also be unreliable. Good DNA analysis starts with good collection, storage, and handling.

Why is sample quality so important in DNA-based forensics?

Poor sample quality can lead to unreliable or meaningless results. DNA work depends heavily on what you start with.

What are SOPs?

SOPs are Standard Operating Procedures. They are strict step-by-step methods that help make sure forensic work is done accurately and consistently.

Why do forensic scientists need to follow SOPs?

Because small mistakes can affect DNA results. SOPs help reduce contamination, poor handling, and unreliable data.

What are common types of biological samples used for DNA?

Blood, semen, saliva, hair, bone, teeth, skin cells, urine, faeces, and environmental DNA.

What biological fluids can contain DNA evidence?

Blood, semen, and saliva. These can be collected and tested to help create a DNA profile.

What tissues or cells can be used for DNA evidence?

Hair, bone, teeth, and skin cells. Some are harder to analyse because the DNA may be old, damaged, or low quantity.

What is touch DNA?

Touch DNA is DNA left behind when skin cells transfer onto a surface. It often contains a low amount of DNA.

Why can touch DNA be difficult to analyse?

It usually has low DNA quantity. It can also vary a lot between people and can degrade over time.

What is environmental DNA/eDNA?

DNA collected from the environment rather than directly from a body fluid or tissue. It may come from traces left in soil, water, or surfaces.

Why is contamination a big issue with small DNA samples?

Because when the sample is tiny, even a small amount of extra DNA can affect the result. This makes careful collection really important.

What are the main steps in biological sample collection?

Locate the evidence, document it, collect it carefully, package it properly, and keep a chain of custody.

Why do investigators need PPE when collecting DNA evidence?

To avoid adding their own DNA to the sample. PPE helps reduce contamination.

What does sterile technique mean in DNA collection?

Using clean tools, gloves, and careful methods so the sample is not contaminated. It helps keep the evidence reliable.

What are examples of DNA sampling methods?

Swabbing, cutting, scraping, and collecting whole items. The method depends on the type of sample and where it is found.

Why is proper packaging important for DNA samples?

It protects the sample and helps prevent contamination or degradation. It also keeps the evidence usable later.

What is chain of custody?

A record of who collected, handled, stored, and transferred the evidence. It helps prove the evidence has not been tampered with.

Why is chain of custody important in forensic DNA?

If the chain of custody is weak, the evidence can be challenged. Good documentation helps the DNA result stay reliable in court.

What can procedural errors do to DNA evidence?

They can create doubt about whether the DNA result is reliable. Even strong DNA evidence can be weakened by poor handling.

What is DNA degradation?

DNA degradation is when DNA breaks down into smaller fragments over time. This can make it harder to get a usable DNA profile.

What environmental factors can degrade DNA?

Temperature, humidity, and UV radiation. These can damage DNA and make it break down.

What biological factors can degrade DNA?

Microbial activity and enzymes. Microbes and enzymes can break DNA down after it is exposed.

What chemical factors can degrade DNA?

pH and oxidation. These can chemically damage DNA molecules.

Why does time matter for DNA degradation?

The longer DNA is exposed to damaging conditions, the more likely it is to break down. Older samples are often more degraded.

What are the main mechanisms of DNA degradation?

Hydrolysis, oxidation, and other chemical modifications. You do not need the full chemistry, just that they break DNA down.

How can DNA degradation be seen in analysis?

More degraded DNA has more small fragments. Larger DNA fragments are less likely to survive.

Why are small DNA fragments a sign of degradation?

Because the DNA has been broken down over time. More small fragments usually means more degradation.

Why do forensic scientists assess DNA degradation?

To see whether the sample is still suitable for DNA profiling. It helps decide what analysis method may work.

How can DNA samples be stored short-term?

Refrigeration or freezing. This slows down degradation.

How can DNA samples be stored long-term?

Deep freezing, freeze-drying, FTA cards, or other solid-phase storage methods.

What is lyophilisation?

Lyophilisation is freeze-drying. It removes liquid from the sample to help preserve it.

What are FTA cards used for?

FTA cards store biological samples, often blood, in a dry stable form. The card absorbs and binds the DNA.

Why does drying DNA help storage?

Dry DNA is usually more stable than wet DNA. Less water means less degradation.

Why might DNA be stored in aliquots?

So the whole sample does not need to be thawed or used every time. This helps preserve the remaining DNA.

What does quality control mean in DNA storage?

Checking that samples are still intact and properly stored. It also includes validation, auditing, and record keeping.

Why is record keeping important for DNA storage?

It shows where samples are, how they were stored, and who accessed them. This protects the reliability of the evidence.

What is a major ethical issue with long-term DNA storage?

People may not fully understand or consent to their DNA being stored long term. This is especially complex when DNA comes from crime scenes.

Why is informed consent complicated in forensic DNA storage?

Some people may not have a real choice, especially suspects or people involved in investigations. This raises ethical concerns.

What is the issue of DNA ownership?

It asks who has control over a person’s DNA once it is collected. This is both a legal and ethical issue.

Why might the right to withdraw DNA from a database matter?

People may want control over their own genetic information. But in practice, removing DNA from databases can be difficult.

What is a potential misuse of stored DNA?

It could be used later for purposes the person did not consent to. Future technology may allow new uses that are hard to predict now.

How could DNA databases affect civil liberties?

Long-term DNA storage could contribute to surveillance. This means people’s genetic information may be monitored or reused.

What are future directions for DNA sample storage?

Better sample stabilisation, better room-temperature storage, DNA encapsulation, and improved methods for degraded DNA.

What is enhanced sample stabilisation?

Methods that help DNA survive longer and stay usable. This can include special substrates, solutions, or storage systems.

Why is room-temperature DNA storage useful?

It avoids needing large freezers. This makes storage cheaper and easier.

What is DNA encapsulation?

A method that protects DNA by enclosing it in a protective material. This may help extend sample viability.

Why is efficiency important in future DNA analysis?

Faster methods can speed up investigations. The goal is reliable analysis of difficult or degraded samples.

What is Rapid DNA technology?

A system that can generate a DNA profile much faster than traditional lab methods. Some systems can produce profiles in about 90 minutes to 2 hours.

What is the benefit of Rapid DNA technology?

It can speed up identification and investigations. It also reduces some delays from sending samples to a lab.

What are examples of uses for Rapid DNA?

Booking/processing, immigration or border control, and disaster victim identification.

How much DNA is in one human diploid cell?

About 6 picograms of DNA. This is a very tiny amount.

Can we get a genotype from one cell?

In theory, yes. In practice, it is very unreliable and often does not work well.

How much DNA do many DNA typing protocols ask for?

About 1 nanogram of DNA. This is roughly around 160 cells worth of DNA.

How much blood may be enough for normal genotyping?

About 0.4 microlitres of blood can be enough. Only white blood cells contain DNA, not red blood cells.

Do red blood cells contain DNA?

No, mature red blood cells do not contain DNA. White blood cells are the blood cells that contain DNA.

Why can blood be a good DNA source even in small amounts?

Because blood contains white blood cells, which contain DNA. Only a small volume may be needed.

What are the main problems with touch DNA?

Low quantity, high variation, and degradation. It can also be affected by environmental exposure.

Why does touch DNA vary between people?

People shed different amounts of cells/DNA. Some people leave more touch DNA than others.

What happens to touch DNA after environmental exposure?

It can degrade over time. Heat, moisture, sunlight, and microbes can reduce DNA quality.

What is DNA from hair usually taken from?

The follicle/root if present. The hair shaft can also contain DNA, but it is usually lower quality.

Why is hair follicle DNA better than hair shaft DNA?

The follicle contains cellular material. Hair shafts often have less DNA and the DNA may be more degraded.

Can DNA be obtained from hair shafts?

Yes, but it is lower quality and harder to analyse. It may still be possible with advanced methods.

What are mixed DNA samples?

Samples that contain DNA from more than one person. These are harder to interpret because multiple profiles overlap.

Why are mixed DNA samples difficult?

Because the DNA peaks/alleles from different people can overlap. It can be hard to work out who contributed what.

What is standard analysis for mixed DNA?

Analysing the whole mixture together. This can be difficult when several people contributed DNA.

What is single-cell analysis?

Separating individual cells and analysing them separately. This can help identify individuals within mixed samples.

Why might single-cell analysis help mixed samples?

It separates the contributors before profiling. This can make it easier to work out whose DNA is present.

What is the golden rule of DNA sample handling?

Rubbish in, rubbish out. Bad samples or sloppy handling lead to bad or unreliable results.

What are the key things that protect DNA evidence quality?

Sterile collection, good storage, proper packaging, chain of custody, and careful documentation.

Why can DNA evidence still be challenged even if the profile matches?

Because the result depends on how the sample was collected, stored, and handled. Poor procedure can create doubt.

What are high-yield DNA sources?

Samples like blood and semen that often contain more usable DNA. These are usually easier to profile than trace samples.

What are challenging trace DNA sources?

Touch DNA, hair shafts, and environmental DNA. These often have low quantity or degraded DNA.

What is the main point of this lecture?

DNA evidence is powerful, but only if the sample is collected, stored, and handled properly. Poor technique can ruin the reliability of the result.