Forensic investigations and analysis of dna

Forensic investigations and analysis of DNA

Police launch enquiries after two bodies found in two days

Police discovered the body of a woman in a flat on the Walsall Road late yesterday afternoon after neighbours became concerned that music had been playing continuously for several days. Officers forced entry into the flat and found the woman’s body. It is thought she had only been dead for a short time.

Police sources last night said they were not treating the death as suspicious.

Only 16 hours later a second body was found. A lady out walking her dog spotted the body in the woods bordering the Star Land. The body of a man dressed in sports wear had clearly been there for some time. Mrs Smith who found the body is still in a state of shock.

A police spokesman said they did not know the identity of the man and were treating the incidence a suspicious.

Autopsies are due to be carried out on both bodies to ascertain the causes

of death

What is forensic science?On finding any body police must first answer

three basic questions:• Who is the dead person?• When did the victim die?• Ho did the person die?

Forensic science provides the tools with which to help answer these questions.

Identifying the body

• Fingerprints

• Dental records

DNA Profiling

• Also known as genetic/DNA fingerprinting• Relies on the fact that apart from identical twins

– everybody’s DNA is unique.• Human genome has 23,000 genes• Each gene has an average 3000 base pairs per

gene ( = 7x107 in total)• But there are over 3 million base pairs• Large amount of DNA does not code for

proteins.

• Coding blocks of DNA = Exons• Non-coding blocks of DNA = Introns• Introns are made up of short DNA sequences

repeated many times • The sequences of repeated bases = Short

Tandem Repeats (STRs) or SATELLITES• 2 main types of STRs – 2-50 base pairs (mini satellite) repeated 50 to

several hundred times - 2-4 base pairs ( micro-satellite) repeated 5-15

times.

• The STRs appear at the same locus on each homologous chromosome

• Number of repeats varies as different patterns inherited form mother and father.

• More closely related – the more similar are DNA patterns

Stages

• Blood or tissue sample is obtained• Treated with detergent to rupture cell membrane

and obtain DNA• DNA is split into fragments using restriction

endonuclease enzymes• Gel electrophoresis is used to separate the fragments

Gel Electophoresis

• DNA samples move towards the positive anode (DNA is negative) at different rates depending on

• Mass and charge • DNA ladder or marker is added – contains fragments of known length

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