4.1.3Additional lessons
Electrophoresis and PCR: Applications — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 29 of 101
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.
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.
| Application | What is compared |
|---|---|
| Crime scene | Suspect and evidence profile |
| Paternity | Child, mother and possible father |
| Identification | Remains and relatives |
| Wildlife trade | Seized 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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