DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ1.b

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Date May 2022 Marks available [Maximum mark: 5] Reference code 22M.2.SL.TZ1.b
Level SL Paper 2 Time zone TZ1
Command term Describe Question number b Adapted from N/A
b.
[Maximum mark: 5]
22M.2.SL.TZ1.b

Describe how DNA profiling can be used to establish paternity.

[5]

Markscheme
  1. DNA sample is collected from the child and its (potential) parents;
  2. from saliva/mouth swab/blood/other body cells;
  3. PCR used to amplify/produce more copies of the DNA;
  4. short tandem repeats/genes consisting of a repeating sequence of bases repeats copied/used;
  5. number of repeats varies between individuals;
  6. unlikely that two individuals have same number of repeats for every gene included;
  7. gel electrophoresis used to separate DNA fragments according to length/number of repeats;
  8. gel electrophoresis generates a unique pattern of bands
  9. DNA profile is the pattern of bands / diagram showing pattern of bands as in a DNA profile;
  10. all bands in the child’s profile must be in one of the parents’ profiles / OWTTE;
Examiners report

Answers to this question were very variable, with some very well-informed accounts including the use of genes containing of tandem repeats and details of the collection of DNA samples from both parents and the child. There were also many accounts with errors of understanding. A common misconception is that paternity is established by finding the male whose profile has most similarities to that of the child. This does not prove that a man is the father of the child and instead the father's profile must contain all bands in the child's profile that do not occur in that of the mother. 

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