These are detailed Revision Notes for Topic 6.1.3 of OCR A-Level Biology (Manipulating Genomes). They were written by me using a combination of the textbook and class notes. I will also be uploading the other topics and creating bundles.
Topics Included:
- DNA profiling
- DNA sequencing and an...
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Manipulating Genomes
21.1 DNA Profiling
21.1 DNA profiling
- A genome is all of the genetic material that an organism
contains 21.2 DNA sequencing and analysis
- Exons are the coding parts of DNA 21.3 using DNA sequencing
- Non-coding regions of DNA are called introns and they are
removed from mRNA before it is translated. 21.4 genetic engineering
- Producing an image of the patterns in DNA is known as DNA 21.5 gene technology and ethics
profiling.
- You have variable number short tandem repeats (VNTRs) which are 20-50 base pairs and are repeated
50-100s of times and they are called minisatellites
- Short tandem repeats (STRs) 2-4 base pairs, called microsatellites
- You inherit half of your VNTRs and STRs from each parent
- Producing a DNA profile
o Extracting the DNA
o Digesting the sample using restriction endonucleases
o Separating the DNA fragments by electrophoresis
o Southern blotting
o Hybridisation
o Visualisation
Polymerase Chain Reaction:
- PCR is a widely used techniques for the selective amplification of particular DNA sequences, such as
individual genes.
- It is used in DNA profiling to amplify microsatellites.
- Quick and sensitive and robust. Is particularly useful when dealing with small amounts of DNA or where
rapid screening is required.
- Method:
o A sample is treated with detergent to break open cells and release DNA
o DNA polymerase, DNA primers with fluorescent marks and nucleotides are added to the
reaction tube
o The reaction tube is placed into the PCR thermal cycler
o The DNA separates into two strands
o Primers (with fluorescent markers) attach at the start of the satellite repeated sequence.
o DNA polymerases attach, nucleotides are added extending the DNA from the primer. The
satellite repeated sequence and DNA adjacent is replicated.
o Then the
DNA strands separate again
o Primers attach at the start of each satellite sequence
o DNA polymerases attach and replication occurs from each primer.
o In each following cycle the process is repeated producing copies of the satellite fragment,
millions are produced and can be separated by gel electrophoresis.
- Denaturation (separation of DNA strands) at 90oC
- Primer annealing at 55oC
- Primer extension at 72oC
- The enzyme must be thermostable, ‘Taq’ polymerase is used
- The number of DNA molecules is doubled during each cycle, producing a rapid increase in the number of
copies.
Uses of DNA profiling:
- Identification of criminals
- Paternity testing
- To identify Nazi War Criminals
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