DNA fingerprinting and forensics

PCR has numerous applications :

1) Gene isolation

2) Mapping of complex traits

3) Molecular taxonomy

4) Forensic science ( DNA fingerprinting)

5) Isolating ancient DNA sequences

6) Diagnosis of inherited disease.

DNA fingerprinting and forensics

Professor Sir Alec Jefferys of Leicester University realised in 1983 that VNTR variation due to the presence of different numbers of microsatellite repeat sequences at the same chromosomal location could be used to distinguish between individuals in a population………

DNA fingerprinting and forensics

DNA fingerprinting:

DNA fingerprinting is based on the fact that large portionsof the eucaryotic genome consists of repetitive, non-coding sequences.

These repeat sequences are found all over the genome, on each chromosome and consists of repeats of the same sequence.

VNTR’sV ariableN umberT andemR epeats

DNA fingerprinting and forensics

VNTR’s are based on the existence of microsatellite repeat sequences

These are repeats of small sequences e.g. CACA

These repeats are scattered throughout the genome:

CACA CACA CACA CACA CACA CACA - Person A

CACA CACA CACA CACA – Person B

DNA fingerprinting and forensics

DNA fingerprinting is based on the fact that individuals in a populationhave different numbers of repetitive sequences at the SAME locus.

DNA fingerprinting and forensics

DNA fingerprinting and forensics

The principle of DNA fingerprinting is VERY SIMPLE:

Use PCR primers which amplify across the variable region:

In different individuals, bands of different sizes will beamplified from the genome

This leads to the fingerprint – unique for every individual.

DNA fingerprinting and forensics

PCR in Forensic science

DNA fingerprinting and forensics

Which child is least likely to be the biological offspring of this couple?

Paternity profiling:

DNA fingerprinting and forensics

Rape Investigation:

1. Known blood sample of victim 2. Known blood sample from defendant 3. DNA size markers 4. Female fraction from vaginal swab of victim 5. Male fraction from vaginal swab of victim.

Q – is the suspect (2) guilty?