DNA profiling: method and uses

In a nutshell

DNA profiling is widely used in forensic science and medical diagnosis. DNA profiling focuses on tandem repeats, which are repeated segments of DNA that do not code for proteins.

Tandem repeats

Definition

Tandem repeats are repetitive segments of non-coding DNA. They are usually made up of $10-100$ bases and they are repeated a different number of times in different people.

Short tandem repeats (STRs) are highly variable and are around $2-5$ bases long. Usually, $13$ STRs are analysed at the same time. Each STR is present in between $5-20\%$ of individuals. However, the chances of two people sharing every STR analysed is one in a quintillion ( $1\times 10^{18}$ ).

Example

A repeated motif could be ATAG and this could be repeated four times in an individual. Therefore, a section of their DNA sequence would read ATAGATAGATAGATAG. Another individual may have seven repeats of the motif. This can therefore be used to distinguish between people.

Making a DNA profile

1.	Collect a DNA sample and isolate the DNA. Example DNA can be collected from blood, skin cells and saliva.
2.	Using appropriate primers and PCR, amplify the section of DNA containing the STRs.
3.	Run the PCR products on an electrophoresis gel.
4.	Compare the banding patterns.

Example

Biology; Manipulating genomes; KS5 Year 12; DNA profiling: method and uses

A DNA profile was constructed from DNA found at a crime scene (CS). DNA from three suspects was taken. Suspect 2. has the same banding pattern to the crime scene profile. The number and location of the bands is the same. Therefore, suspect 2. is guilty.

Uses of DNA profiling

Use	Explanation
Forensic science	DNA profiling is commonly used during criminal cases to match suspects to DNA obtained from crime scenes.
Maternity and paternity profiling	DNA profiling can be used in maternity and paternity testing as half of a child's genetic information derives from each of their parents.
Plant and animal breeding	Plants or animals with a particular allele of a desirable gene can be used for breeding to increase the probability of their offspring having the desired characteristic.