IBDP Biology - DNA Profilling

In this IBDP Biology topic, you can learn different biotechnology method.

• Introns – the regions of the chromosomes which are used in DNA profiling.
• Mini-satellites – 20-50 base sequence repeated from 50 to several hundred times.
• Micro-satellites – 2-4 bases repeated between 5 and 15 times.
• The more closely related the two individuals, the more similar the DNA patterns are.

• DNA is extracted from a blood or cell sample.
• It is split into fragments using restriction enzyme.
• These cut the DNA at certain points in the intron sequences.
• Each type cuts a DNA molecule into fragments at different recognition sites.

• The fragments are placed in wells in an agarose gel medium in a buffering solution, with known DNA fragments.
• The gel contains a dye which binds to the DNA fragments in the gel.
• A dye is also added to the DNA samples.
• An electric current is passed through the apparatus and the DNA fragments move towards the positive anode.
• The plate is placed under UV light.
• The DNA fluoresces so it can be identified.

• An alkaline buffer solution is added to the gel after electrophoresis.
• A nylon filter or (nitrocellulose paper) is placed over it.
• Dry absorbent paper is used to draw the solution containing the fragments from the gel to the filter, leaving ‘blots’ on it.
• The alkaline solution also denatures the fragments so the strands separate and the base sequences are exposed.

• These are short DNA sequences that are complementary to specific sequences which are required.
• Hybridisation - large amounts of the probe are added to the filter and bind with the complementary DNA strands.
• Excess probes are washed away.
• X-ray pictures are taken of the filter or the filter is placed under UV light.

The reactants:

1. DNA sample
2. DNA polymerase (enzyme)
3. Primers
4. The four nucleotide bases

1. The reactants are placed in a vial in a PCR machine.
2. Mixture is heated to 90-95°C – which causes the DNA strands to separate as the hydrogen bonds between them break down.
3. Mixture is cooled to 50-60°C – the primers bind (anneal) to the single DNA strands.
4. Mixture is heated to 75°C – the optimum temperature for the enzyme to build the complementary strands of DNA.

This is the end of the topic

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Drafted by Eva (Biology)

Photo references:

1. https://www.youtube.com/watch?v=YF0UaIB0QpE
2. https://ib.bioninja.com.au/standard-level/topic-3-genetics/35-genetic-modification-and/gel-electrophoresis.html
3. https://www.mun.ca/biology/scarr/Gr12-18.html
4. https://zh.wikipedia.org/zh-hk/File:Polymerase_chain_reaction-en.svg