Topic 6, Biology, Edexcel SNAB markschemes and model answers

  • Created by: Summer
  • Created on: 20-12-13 13:23

Topic 6: Immunity, Infections and Forensics

DNA Profiling

Polymerase is the…. enzyme used in the Polymerase Chain Reaction to amplify DNA in a small sample of blood taken from a crime scene.


Gel Electrophoresis is the …..process used to separate DNA fragments to create a DNA profile    


Describe how gel electrophoresis can be used to analyse DNA. (3)

First, a DNA sample will be collected from blood, saliva or semen etc; these small samples of DNA can then be amplified by PCR. DNA profiling then takes place which uses *restriction enzymes to break the DNA and then *uses electro potential difference, with the DNA in a gel, to draw the bands apart. *The DNA is stained so it can be seen and will *show up as bands/bars. *The number of bands that match indicates the similarity of the DNA.



Name substances X, Y and Z:

Substance X ...........DNA Primers

Substance Y......... (mono)nucleotides

Substance Z ..........DNA Strands


What are the temperatures for?

T1: Heated to 90–95 °C

T2: Cooled to 55–60 °C

T3: Heated to 75 °C














Using DNA profiling explain how a suspect is found guilty. (5)

A DNA match is needed, this means that *all of the bands in the sample are the same as the ones shown in the evidence sample. *DNA profiling assumes every individual’s DNA is unique/different; *apart from identical twins. *DNA profiling analyses the introns/noncoding blocks/STR parts of DNA as the *non-coding areas are hypervariable because *there are a large number of introns/non-coding blocks and so there can be *many combinations of STRs at each locus.


Suggest how DNA profiling could be useful to scientists who examine fossils of animals and plants. (2)

Comparisons could be made between DNA from fossils and other organisms to find genetic relationships/how closely related they are. It may also be *used in taxonomy/classification *to understand evolutionary lines/to determine a common ancestor.

Explain how the results of DNA profiling of tissue samples from the two sub-species could be used to provide evidence that they share common ancestry. (3)

DNA profiling will *produce bands that will have spread to *certain positions. *Common/similar bands will contain similar DNA fragments; *the more similar these patterns, the closer the relationship/more likely the sub-species will have a recent common ancestor. *There will still be very few differences between the DNA of sub-species.


Suggest how DNA analysis could give further evidence for evolution. (2)

DNA analysis could show the *similarity (of DNA) and indicate the closeness of a genetic relationship *because genes are sections of DNA and these *genes are the codes for proteins.


Why can’t species of plants be identified from woody (xylem) material using PCR and DNA profiling? (2)

Because *xylem/wood is made of dead material/has no living material/cytoplasm/nuclei/ mitochondria, meaning *no DNA


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