SME
Grade 9 Science · Problem type
DNA fingerprinting
Use this for “Which suspect’s DNA matches the evidence?” or “Could this man be the father?”
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Shorter pieces run farther toward +.
DNA from blood at the scene and from three suspects is cut by the same enzyme and run side by side.
The ladder’s pieces of known length give the scale.
Assumptions
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Restriction enzymes cut DNA at set sequences; the lengths of the pieces differ from person to person.
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Only identical twins share every band; a child gets each band from the mother or the father.
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The pieces run through a gel toward +, the shorter ones farther.
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Genes switched on and off
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Evidence for evolution, population genetics and speciation
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Related lessons
Mutations, gene expression and biotechnology
Main lesson
An insertion shifts the reading frame
Use this for “Why does inserting one base change every amino acid after it?”
A deletion shifts the reading frame
Use this for “One base is deleted from a gene. Which codons change, and is there still a stop codon?”
Gel electrophoresis: a piece of DNA cut once
Use this for “A 5,000 bp piece is cut once, and one fragment is 3,000 bp. How long is the other?”
PCR: copies double each cycle
Use this for “Starting from 2 copies, how many copies are there after 10 cycles of PCR?”
Silent, missense, nonsense or frameshift?
Use this for “The codon GAA changes to GUA. What kind of mutation is it?”
Which DNA tool is it?
Use this for “Which technique would make millions of copies of DNA from one hair?”
Genes switched on and off
Use this for “Why does a bacterium make the enzymes for lactose only when lactose is there?”