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4.1.3Additional lessons

Electrophoresis and PCR: Applications — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 29 of 101

📚 IB Biology HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 4DNA Profiling

Idea
  • Idea Every person except identical twins has a unique pattern of repeated sequences in their DNA, which can be used like a fingerprint.
Short tandem repeats
  • Short tandem repeats STRs are short sequences repeated one after another, and the number of repeats at a locus differs between individuals.
Method
  • Method DNA is extracted, selected STR regions are amplified by PCR, and the fragments are separated by gel electrophoresis.
Reading the result
  • Reading the result The pattern of bands, or peaks, from a sample is compared with the pattern from a known individual.
Small samples
  • Small samples Because PCR amplifies DNA, a profile can be made from a tiny amount of blood, hair or saliva.

Part 2 of 4Uses of DNA Profiling

Uses of DNA Profiling
Forensic science
  • Forensic science Profiles from DNA at a crime scene are compared with those of suspects, and a match places the person at the scene.
Paternity testing
  • Paternity testing A child inherits half of the bands from each parent, so every band in the child must be present in the mother or the father.
Identifying remains
  • Identifying remains Profiles of unknown remains are compared with those of relatives to identify disaster victims.
Species and disease
  • Species and disease DNA analysis can identify species, such as illegally traded wildlife, and detect pathogens or inherited mutations.

Part 3 of 4Interpreting and Evaluating Results

1
Examine the lanes on the gel and look for bands at the same position in the sample and reference lanes.
2
A sample matches a suspect only if all the bands match, and one non-matching band excludes the person.
3
For paternity, check that each band of the child comes from either the mother or the alleged father.
4
Judge the strength of the match by considering how common the pattern is in the population.
5
Consider limits, such as contaminated samples, mixed DNA from several people and ethical issues of storing databases.
ApplicationWhat is compared
Crime sceneSuspect and evidence profile
PaternityChild, mother and possible father
IdentificationRemains and relatives
Wildlife tradeSeized sample and known species

Part 4 of 4Exam Checklist & Tips

4.1.3 – Key Points for the Exam

  • DNA profile A pattern of DNA fragments characteristic of an individual.
  • Short tandem repeat A short DNA sequence repeated several times in a row.
  • Locus The position of a gene or sequence on a chromosome.
  • Forensic Relating to the use of science in legal investigations.
  • Contamination Unwanted DNA entering a sample.

Common Mistakes

  • Saying a DNA profile shows the entire genome, when it shows a few selected regions.
  • Claiming that a match proves guilt, although it only shows the DNA came from that person.
  • Forgetting that children get half of their bands from each parent.
  • Ignoring contamination as a possible source of error.

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