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CAIE A-Level Biology A2 19.1.9 Gel Electrophoresis Questions

Use real exam gels to explain why shorter DNA fragments travel further, then compare bands with controls or ladders to identify fragment sizes, alleles and deletions.

Syllabus
2028–2030
Course
Biology 9700
Level
A2

Exam points

  • Explain how negatively charged DNA fragments move towards the anode through a gel and why shorter fragments migrate faster and further than longer fragments.
  • Interpret DNA band positions and fragment numbers to infer allele differences, genotypes, restriction-site changes or successful gene deletion.
  • Use control lanes or a DNA ladder to validate a gel, estimate fragment length and identify an allele, genotype or phenotype from band patterns.

CAIE A-Level Biology A2 19.1.9 Gel Electrophoresis Questions question 1

[Maximum number: 3]

Traditional techniques for genetically modifying organisms use three enzymes:
- restriction endonuclease
- reverse transcriptase
- DNA ligase.

For example, these enzymes have been used to produce genetically modified (transgenic) pigs containing the GFP gene coding for green fluorescent protein, originally sourced from jellyfish.

Fig. 5.1 shows the results from a second trial of the new technique, analysed by electrophoresis.
- Lanes 1-4 show DNA from four pigs born after Cas9 nuclease was used to cause a deletion in a target gene coding for a cell surface protein.
- Lane 5 shows DNA from their surrogate mother.
- Lane 6 shows DNA from another normal pig for comparison.

The size of the DNA fragments is given in kilobase pairs (kbp) as shown in Fig. 5.1. 1 kbp is 1000 base pairs of DNA.

The target gene measures 6 kbp and codes for a cell surface protein that is essential for the disease virus PRRSV to infect cells in the pig's body.

Fig. 5.1

Fig. 5.1

Explain what Fig. 5.1 indicates about the success of the new technique in causing a deletion in a gene in pigs so that they show resistance to PRRSV.

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