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The Man Who Caught a Million Criminals

Invention of DNA Fingerprinting

dna
Speaker(s)

Ian Goodhall

Presentation Date

January 22, 2024

Lynn’s Review

Ian, biology teacher and previously Head Teacher at Yateley School (the largest secondary school in north east Hampshire), found no issues of class behaviour at Science at Fishbourne. We were a captive audience, and many comments were made that this presentation was at a good level for the group. I have found many links to websites (below) for further investigation and information, as so many aspects of DNA were covered in this presentation.

Here I offer short summaries of each area:

Genetic Fingerprinting

Alec Jeffreys discovered the technique of genetic fingerprinting whilst working in the department of genetics at Leicester University in 1984.

The first crime where this technique was used was in 1986. The police had arrested a young man with learning difficulties, believing him to be a serial killer. Using the new technique of DNA fingerprinting, DNA samples from all men, local to the crimes, who had been born between 1953 and 1970 were collected and tested. No matches were found, and no match was found with the arrested young man.

A year later, from a chance conversation amongst friends, it was discovered that the man responsible for the crimes had sent someone else to impersonate him, when DNA was collected. He was subsequently found guilty of the crimes and of 1000 further sexual offences. He was sent to prison for 30 years.

There is now a UK database of 5 million samples of DNA.

DNA

DNA is a robust molecule. Each molecule consists of two long polynucleotide chains composed of four types of nucleotide sub units. The base may be either: adenine (A), cytosine (C), guanine (G), or thymine (T).

The non-coding areas of DNA have repeated letters (combinations of G,C,A,T) and the position and number of repeats is unique to each person. 97% of DNA is Non-coding DNA.

A DNA molecule is composed of two DNA strands held together by hydrogen bonds between the paired bases.

The process of DNA profiling:

  • Enzymes are used to cut up DNA into fragments

  • Fragments are put onto agarose gel

  • Negatively charged DNA migrates through the pores of an agarose gel towards the positively charged end of the gel when an electrical current is applied, with smaller fragments migrating faster. The resulting bands can then be visualized using ultraviolet (UV) light.

  • The resulting bands shown have a 30 billion to one chance of being the same as those of another person, except in the case of identical twins.

  • The possibilities for uncertainty when using this to discover who committed a crime are commented on in the fifth website link below.

PCR

PCR (Polymerase Chain Reaction) is a process that can amplify a tiny sample of DNA in order to read the repeating letter patterns in a DNA molecule.

DNA samples are treated to break the DNA strands. These are copied in the process. Repeats of the procedure (cycling) produce more copies: 4 cycles will create 32 copies.

DNA fingerprinting has many uses and Ian explained how this process had been used to identify the remains of King Richard 3rd, and The Romanovs. It can also help to solve issues of paternity.

History

In 1869 Frierich Mieschner discovered DNA without fully realising the role it played.

In 1944 Oswald Avery discovered that DNA, rather than proteins, controls life, (only DNA can convert TB bacteria into a non- lethal strain, so proving that DNA is a genetic molecule).

Rosalind Franklin Photograph 51. In 1952 Rosalind Franklin, together with her PhD student, Ramond Gosling, exposed DNA to X-rays for a total of 62 hours and achieved Photograph 51. This was shown to Francis Crick, who was trying to build a 3D model of DNA with James Watson. They achieved their model in 1953 and were recognised for the discovery, receiving the Nobel Prize in 1962. Only much later has Rosalind Franklin received merit for her research. She died at the age of 37, unacknowledged, from ovarian cancer, possible caused by exposure to X-rays.

Photograph 51

Epigenetics

Epigenetics is a way of influencing how our genome is regulated without the DNA code itself being changed. Epigenetics can determine when genes are turned on and off (also referred to as gene expression), and which proteins are produced as a result. It can even control the structure of the genome.

Most epigenetic modifications are transient and reversible, allowing our cells to respond and adapt to changes in environment and behaviour. Although they happen on a molecular level, they can have a considerable impact on us, and can also be influenced by external factors, such as diet and lifestyle.

Summary of Genetic Fingerprints

  • These exist in blood, bone, hair follicles, saliva, semen, skin and sweat.

  • They are the same in every cell and retain their distinctiveness throughout a person's life.

  • Human cells contain 23 chromosomes (packets of DNA) from the father and 23 from the mother.

  • Each DNA strand contains a unique sequence or code of genetic information. But while most of DNA shows only slight variation from one person to the next, certain areas, called 'minisatellites' (short sequences of chemical building blocks) show variation in the numbers of repeat units (or stutters) unique to each person.

  • DNA information can be recovered from human and animal remains as far back as Neanderthal man, and has been used to solve a number of high profile mysteries from the past, including the identification of Josef Mengele's skeleton and the identity of children of US President Thomas Jefferson's children by one of his slaves.

Apart from identification, paternity and immigration cases, the technique is also used in medical research including cancer and genetic conditions such as Huntington's disease.

Below are links to websites for more information.

  • The first link is a very useful one. It gives much information on DNA profiling and on Alec Jeffreys.

  • The second link to a YouTube video, gives clear information on PCR testing and includes snippets about its inventor. (There are several YouTube videos of Kary Mullis if you search for them).

  • The third link is a BBC Bitesize about the PCR process

  • The fourth link gives information on Rosalind Franklin’s discovery and Crick and Watson’s model of the double helix.

  • The fifth and sixth highlight possible issues with DNA Fingerprinting

More links that may be of interest

https://www.britannica.com/science/recombinant-DNA-technology

https://www.britannica.com/science/polymerase-chain-reaction