Genetic profiling

In the human genome, there is a small amount of DNA that is unique to individuals. By cutting a sample of DNA into fragments and separating the fragments by size, it is possible to make a characteristic profile of DNA bands for individuals.

This technique is called DNA profiling, and is a technique that can be used to determine paternity, or help solve crimes where the suspect may have left a sample of body tissue at the crime scene.

It can also be used in other organisms to compare different species for classification purposes.

How to produce a DNA fingerprint

Isolation – separate the DNA from other tissues.
Fragmentation – use an enzyme to break the DNA into short lengths.
Separation – pass an electric current across a layer of gel which has the DNA fragments at one end. The fragments will move different distances across the gel. This is called gel electrophoresis.
Comparison – match the pattern of fragments on the gel with other samples of DNA.

Using DNA profiling in solving crimes

DNA from a crime scene labelled as Crime scene, Victim, Suspect A, Suspect B

DNA is often left at the scene of a crime. It is found in blood, skin, and even hair. Once the DNA has been isolated from the victim, and if suspects have been identified, then DNA profiling can be useful in placing a suspect at the scene of the crime.

Question

In the example above, which suspect has left their DNA at the crime scene?

Using DNA profiles to determine paternity

DNA from a paternity test labelled as Baby, Mother, Father A, Father B

To determine paternity, the DNA profile of both the baby and its mother must be known. Any band found in the DNA profile of the baby that cannot be attributed to the mother must be present in the DNA profile of the father for paternity to be confirmed.

Question

In the example above, is the father of the baby Father A or Father B?

DNA profiles can also be used to identify alleles associated with particular genetic disorders. Testing of newborn babies uses this technique to look for disorders such as cystic fibrosis. The early identification of genetic disorders such as these results in early treatment, which can then reduce the impact of the disorder on the sufferer’s life.

Genetic profiling can be controversial. The table below summarises some of the advantages and disadvantages of using this technique.

Advantages	Disadvantages
DNA evidence is reliable as it is highly unlikely that two people would share the same profile, except in the case of identical twins	Stored DNA data might get into the hands of insurance, loan companies or employers who could analyse your DNA for predisposition to disease and refuse your business because of it
DNA profiles can be used to determine paternity	Storage of DNA profiles can be seen as an invasion of privacy
DNA profiles can be used to identify genetic disorders early	Theft of DNA profiles from a database is a real threat
DNA profiles can be used to place suspects at a crime scene	It is possible to plant DNA at a crime scene giving false evidence, or an innocent person’s DNA might be at the scene even though they had nothing to do with the crime

Advantages	DNA evidence is reliable as it is highly unlikely that two people would share the same profile, except in the case of identical twins
Disadvantages	Stored DNA data might get into the hands of insurance, loan companies or employers who could analyse your DNA for predisposition to disease and refuse your business because of it

Advantages	DNA profiles can be used to determine paternity
Disadvantages	Storage of DNA profiles can be seen as an invasion of privacy

Advantages	DNA profiles can be used to identify genetic disorders early
Disadvantages	Theft of DNA profiles from a database is a real threat

Advantages	DNA profiles can be used to place suspects at a crime scene
Disadvantages	It is possible to plant DNA at a crime scene giving false evidence, or an innocent person’s DNA might be at the scene even though they had nothing to do with the crime

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DNA and inheritance – WJECGenetic profiling