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What is DNA?Every cell in every living thing (or organism)has DNA, a molecule that contains all theinformation about that organism. Lengths ofconnected DNA molecules, called genes, aretiny pieces of a code. They determine whateach organism is like in great detail. Almostall the DNA and genes come packaged inthread-like structures called chromosomes(humans have 46). There are 22 almostidentical pairs, plus the X and Y chromosomes,which determine if a human is male (one Xchromosome and one Y chromosome) orfemale (two X chromosomes).

Genes are passed on from parents tochildren, and no two organisms (except clonesand identical twins) have the same DNA. Many

things – the colourof your eyes orhair, whetheryou're tall or short,your chances ofgetting certaindiseases –depend on thegenes you getfrom your parents.Half of your genescome from yourmom and halfcome fromyour dad.

What is DNA profiling?The exciting possibilities of the fact that each personhas a unique DNA “fingerprint” (scientists call it aprofile) was first realised in 1984 by the British scientist,Alec Jeffreys. Two years later, American scientist KaryMullis developed the PCR (polymerase chain reaction).This is a process that scientists can use to multiplysmall amounts of DNA so they can study it more easily.

For example, let's say that someone has broken intoa store and accidentally got cut on a broken window,leaving a very small amount of blood behind (whatscientists call “trace elements”). Before 1986scientists might not have been able to extract anyDNA for analysis from the blood on the glass becausethere was too little blood. But with PCR they can nowtake that small amount and copy it over and overagain, making the extraction of the DNA foranalysis much easier.

Basically, DNA profiling is the matching up ofindividuals' DNA profiles. Let's use the above exampleof the store robber. The police find a suspect and getthem to give a DNA sample (this could come fromsaliva or blood). They then send it to the laboratorywhere this sample is compared with the sample takenfrom the window. If the samples match, then it is likelythat the suspect is the one who robbed the store; ifthey don't match, then the police know they've gotthe wrong person.

It is virtually impossible for one person to have thesame profile as someone else in the world, unlessthey are identical twins. So, if a lab matches twoDNA samples they can only be from one person.

More usesDNA profiling doesn't only have to be used to catch criminals.It can also help doctors in finding out if a child might get adisease that their parent has, or for a court to determinewhether or not someone is really another person's mother,father, sister or brother. And DNA is not only used foranalysis in humans, but also other organisms likeplants, animals and even bacteria.

In South Africa the police's forensics laboratory uses tests,which limit the sequence to one person in a billion whowill have that exact pattern. In places like England,forensic scientists use tests which limit the patternto one person in a trillion.

DNA can help people in conservation management. In SouthAfrica, many universities are finding ways of using DNA profilingto identify animals and plants for conservation, and in preventingpoaching of animals like rhino and elephant. DNA profilingcan also help in tracing pollution outbreaks and infectiousdisease research.

In other parts of the world, databases of the DNA of catsand dogs have been set up. These have actually helped tosolve criminal cases where, for example, a cat's hair wasfound at a crime scene and could be linked to its owner.

Another use forDNA profiling inSouth Africa is inlooking at theDNA found in theorganisms thatcause HIV/AIDSand TB. If scientists canunderstandthe DNA better,they might be able to find a cure.

DNA profiling in the futureScientists hope that they will one day be able to not onlyuse DNA to match people, but to actually form an “identikit”or “photo” of what that person will look like. But this mightstill take some time as it is not yet possible for scientists towork out tests to identify with 100% certainty things like eye,hair, or skin colour.

Scientists are also hoping that they will one day be ableto identify people through the DNA of the tiny bugs that liveon our skin. They believe this will help to distinguish evenidentical twins, as each person has a different kind ofbug-population that co-habits with them.

The study of DNA and DNA profiling is always growingand improving. And it can help scientists to understandmany things about all living organisms that theynever knew before.

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DNA (deoxyribonucleic acid) is whatmakes you, YOU. It's what makeseveryone special and unique. And it can help scientists

discover all sorts of things like how to diagnose and treatgenetic diseases (diseases passed from a parent to a child),

or help the police catch a criminal.

DNA fact fileBy: Professor Valery Corfield

DNA stands for deoxyribonucleic acid.

It is a chemical substance made from buildingblocks that form long, thin strings.

The DNA strings, called molecules, are packedvery tightly into the nucleus of cells.

The DNA molecules twist around each other andform a spiral ladder – the DNA double helix.

DNA double helixes are organised into 23 pairsof chromosomes in every cell in your body.

This set of chromosomes is the instructionmanual to make YOU.

Each different instruction is called a gene.

The gene instructions are written in a DNA code –the genetic code.

New coded copies are made when theDNA double helix unzips down the middleand new molecules are added to eachunzipped strand.

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