DNA profiling

What is the first stage of producing a DNA profile?

Extracting the DNA. Using a technique called polymerase chain reaction (PCR) the tiniest fragment of tissue can give scientists enough DNA to develop a profile

What is the second stage of producing a DNA profile?

Digesting the sample - strands of DNA are cut into small fragments using enzymes called restriction endonucleases. They cut DNA at specific nucleotide sequences, known as restriction/recognition sites

What is the second stage of producing a DNA profile? (2)

All restriction endonucleases make 2 cuts, once through each strand of the DNA double helix. They let DNA be cut at defined points in the introns

What is repetitive DNA? (2nd stage)

Codes for a significant fraction of genomic DNA and is categorised into 3 types: tandem, terminal and interspersed repeats

What is one type of tandem repeat? (2nd stage)

Satellite DNA. It is highly repeated and located mostly in the heterochrmatic region around centromeres and introns

What are mini satellites? (2nd stage)

A sequence of 20-50 base pairs that could be repeated from 50-100 times in the DNA

What are micro satellites? (2nd stage)

A sequence of 2-4 bases repeated between 5-15 times in the DNA

What is the trend with satellite patterns?

Only identical twins have an identical satellite pattern, although the more closely related you are to someone, the more likely you are to have similar patterns

What is the second stage of producing a DNA profile? (3)

Restriction enzymes are used and they leave the satellites intact, so the fragments at the end of the process include a mixture of intact mini and microsatellite regions

What is the third stage of producing a DNA profile?

Separating the DNA fragments - cut fragments of DNA need to be separated to form a clear pattern. This is done using electrophoresis, a technique that influences the way charged particles move through a gel medium due to a current

What is the third stage of producing a DNA profile? (2)

Gel is immersed in alkali in order to separate the DNA double strands into single strands. Single stranded DNA fragment are transferred onto a membrane

What is the fourth stage of producing a DNA profile?

Hybridisation - radioactive or fluorescent DNA probes are added in excess to the DNA fragments on the membrane. They bind to the complementary strands of DNA under specific ph and temps. They identify the microsatellite regions that are more varied than the mini satellite regions

What is the fifth stage of producing a DNA profile?

Seeing the evidence - if radioactive labels were added to the DNA probes, X-ray images are taken of the membrane. If fluorescent labels were added, the membrane is placed under UV light so the tags flow

What is the final stage?

Fragments give a pattern of bars -the DNA profile- which is unique to every individual except identical siblings