DNA profiling Flashcards
Define a polymorphic site.
A point in the genome that s highly variable between individuals.
mtDNA is highly variable and good for DNA profiling. Give one other advantage of using it.
It is available in extremely high copy number per cell so even small specimens from a crime scene can be useful.
Why are Y-chromosomes helpful in sexual assault cases?
Only males carry the Y so if the victim is female her DNA will not contaminate the evidence.
Even though mtDNA and Y-chromosomes are useful in DNA profiling, using autosomes is preferred. Give 4 reasons why.
- Most of our genome is autosomal, thus there is more variation
- Autosomes are highly variable at some loci
- Each locus has 2 copies
- Most loci are un or weakly linked, meaning they assort independently. This creates further variation.
Is there recombination in mtDNA?
No.
Is there recombination of the Y-chromosome?
Very little.
What does VNTR stand for?
Variable number tandem repeats.
Define a VNTR.
A point in the genome where a short nucleotide sequence or ‘motif’ is repeated. The number of repeats vary between individuals.
A.R. Wyman and R. White discovered VNTRs in 1980. When were they first used in forensics?
1984, applied by Alec Jeffreys.
VNTRs come in 2 forms. What are they?
- Minisatellites
2. Microsatellites
Define a minisatellite.
The repeat motif is between 10-50 bp in length.
Define a microsatellite.
The repeat motif is between 2-5bp in length.
Mini and microsatellites are generated in the same way. True or false?
False.
What are satellite bands?
When DNA is centrifuged at high speed it separates according to density. Highly repetitive DNA forms satellite bands.
What solution is the DNA centrifuged in?
CsCl (caesium chloride)
Approx. how many minisatellites are there in the human genome?
1000.
Minisatellites are always different. True or false?
False - they often contain a core sequence that varies in one base position.
The number of VNTRs varies between parents and offspring. This high mutation rate causes variation in the form of what?
Alleles.
Where are most VNTRs found?
In introns (non-coding ‘junk’ DNA).
What can happen if a microsatellite is found in the coding region of a functional gene?
It can create genetic disease.
Give 2 examples of a genetic disease caused by a microsatellite mutation.
- Huntingdon’s disease
2. Fragile X syndrome
What are trinucleotide expansion mutations?
VNTRs containing 3 nucleotides responsible for numerous diseases.
What is characteristic about diseases caused by trinucleotide expansion mutations?
They appear with early onset and increase in severity down the generations.
Give 2 mechanisms by which VNTR numbers can be changed.
- Unequal crossing over
2. Slipped-strand mispairing
