DNA- Technology Flashcards
Who first discovered DNA profiling
Alex Jeffreys
When was DNA profiling discovered?
1984
What was the first application of DNA profiling?
The conviction of Colin Pitchfork
Who murdered and raped a girl
What is DNA?
Unique and hereditary material
(Except identical twins)
Made up of nucleotides- phosphate, sugar, base (CAGT)
The bases make up a genetic code- produces proteins
What is unique about mitochondrial DNA?
It comes from the mother
What are the possible sources of DNA?
Saliva, hair root, cells, blood, semen, urine, tissues, bones, teeth
We hope for a trail, i.e. Fingerprints, weapons and bite marks
How much blood to you need to obtain a DNA profile?
Only a small quantity
What is the RFLP method to obtain a DNA profile?
Restriction fragment length polymorphism
Requires large amounts of DNA, UNDEGRADED-so unlikely in warm conditions
Look for variable number tandem repeats
How does PCR obtain a DNA profile?
Polymerase chain reaction
Requires less DNA that can be partially degraded
Short tandem repeats (1-5 bases, repeated 17 times) analysed
However more sensitive to contamination
How does RFLP occur?
Variable number tandem repeats
Patterns match
Restriction enzymes cut at points of DNA
Separated by gel electrophoresis
How does PCR occur?
Short tandem repeats are copied in many cycles with different temperature changes
95 degrees- DNA separates
Lower temp- primers anneal/bind
72 degrees- taq polymerase synthesises new DNA strand
Why is PCR beneficial?
It can make lots of copies of specific sections of DNA
it can analyse degraded samples of DNA as it makes so many copies
What is done after PCR makes the copies of STRs?
Analyse it through gel electrophoresis
Primers are labelled with fluorescence
Products exposed to laser bear a
What happens in gel electrophoresis?
Smaller sections of DNA travel further through the gel
Thicker bands- same number of repeats for each allele (one from mum one from dad)
What are short tandem repeats?
STR’s
People vary in the number of repeats at STR locus
What are the two DNA profiling methodologies?
RFLP (restriction fragment length polymorphism)
PCR (polymerase chain reaction)
What is the normal appearance of peaks from a DNA profile?
They are coloured because they have a fluorescent molecule attached to them during PCR
What are stutter bars?
DNA repeats slipping out of register during PCR
Usually only 1 repeat length smaller than the main band
Insertion caused by backward slippage
Deletion caused by forward slippage
What is LCN?
Low copy number
Copy 10 informative sites from smaller amounts of starting material
Takes longer as number of cycles has to increase
What is the use of partial profiles?
Used for familial searching (on data base)
Can use lcn profiling
What is SNP?
Single nucleotide polymorphism
What is single nucleotide polymorphism?
Difference in a single base unit Covers 90% of genetic variation Happens during meiosis SNP ever 300 base pairs Helps with phenotyping
What is the use of the Y chromosome in STR testing?
The amelogenin locus (involved in mineralisation of enamel in developing teeth) is 6 bases shorter in the X chromosome than the Y
One peak on X, 2 on Y
What is mitochondrial DNA?
1 mitochondrial has 5-10 identical circular molecules of DNA
