Molecular Forensics > Genetics > Flashcards

Genetics Flashcards

(49 cards)

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1
Q

What are SNPs?

A

A type of molecular marker consisting of a single DNA building block (nucleotide)

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2
Q

Are SNPs a first-choice forensic method?

A

No, they’re occasionally used is another, more common method, fails

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3
Q

What additional value can SNPs provide?

A

Provide additional formation on:
-degraded DNA analysis
-genetic genealogy
- Phenotype information (prediction of physical appearance)

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4
Q

What events can create SNPs?

A
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5
Q

Are SNPs a first-choice forensic method?

A

No, they’re occasionally used if another, more common method fails

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6
Q

What additional value can SNPs provide?

A

Further info about a sample including:
- analysis of degraded DNA
- forensic genetic genealogy
- DNA phenotyping (prediction of physical appearance)

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7
Q

What events can create SNPs?

A

Insertion, deletion and substitution

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8
Q

Where can SNPs form in the genome?

A

Coding regions and non-coding regions

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9
Q

What is a synonymous (silent) SNP?

A

A SNP that leads to no change in an expressed protein

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10
Q

What is a non-synonymous SNP?

A

An SNP that leads to change in an expressed protein

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11
Q

What is a transition SNP?

A

A singe nucleotide polymorphisms where a base is swapped with another of the same type (e.g. purines for purine)

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12
Q

What is a transversion SNP?

A

When a pyrimidine is swapped for a purine or vise versa (different classes)

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13
Q

What does bi-allelic mean in SNPs?

A

When two alleles are formed

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14
Q

What does tri-allelic mean in SNPs?

A

Three alleles formed

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15
Q

What does tetra-allelic mean in SNPs?

A

Four alleles

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16
Q

Are SNPs as polymorphic as STRs?

A

No STRs have fewer alleles- STRs can form 5-20

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17
Q

Why are SNPs compared to STRs?

A

To evaluate their possibility for individual identification

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18
Q

How often do STRs appear in the human genome compared to SNPs?

A

STRs- 1 in every 15kb
SNPs- 1 in every 1Kb

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19
Q

How much information does STRs provide in comparison to SNPs?

A

STRs- High
SNPs- low (only 20% to 30% as informative as STRs)

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20
Q

What’s the mutation rate of STRs compared to SNPs?

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A

STRs- 1 in 100
SNPs- 1 in 100 million

21
Q

What markers do STRs use?

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A

Di, tri, tetra, penta- nucleotide repeat markers with many alleles

22
Q

What marker types do SNPs use?

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A

Mostly bi- allelic markers

23
Q

How many alleles per marker in STRs compared to SNPs?

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A

STRs- 5 to 20
SNPs- typically 2

24
Q

Detection methods of STRs compared to SNPs?

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A

STR- Gell capillary electrophoresis
SNPs- Sequence analysis; microchip hybridisation

25
What’s the multiplex capility of STRs compared to SNPs
STRs- more than 10 markers with multiple fluorescent dyes SNPs- Difficult to amplify more than 50 SNPs well
26
Amplicons size of STRs compered to SNPs (Length of a DNA segment that can be amplified through PCR)
STRs- 75 to 400bp SNPs- can be less than 100mp
27
What can SNPs predict sometimes that STRs can’t?
Ethnicity and Phenotypic information (mainly just hair colour)
28
Advantages of STRs
Many alleles so enables a higher success rate for detecting and deciphering mixtures
29
Disadvantages of STRs
Data interpretation must account for artefacts such as dye blobs, stutter , spikes etc
30
Advantages of SNPs
-PCR products can be made small so it means there may be a higher success rate with degraded DNA samples -low mutation rate -kinship analysis -Phenotype prediction
31
SNPs disadvantage
-No widely established core loci -Large multiplexing assays required -mixture resolution and interpretation issues -multiple typing platforms make universal SNP selection difficulty -Population substructure due to low mutation rate
32
Who declared SNP classification categories?
ISFG
33
What are the four SNP categorises?
IISNPs- Identity SNPs individual identification LISNPs- Lineage SNPs lineage informative AISNPs- Ancestry SNPs ancestry informative PISNPs- Phenotype SNPs Phenotype Informative
34
Characteristics of IISNPs
SNPs that collectively give very low probabilities of two individuals have the same multi-locus. Genotype
35
Characteristics of LSNPs
Sets of tightly linked SNPs that function as multi allelic markers that can serve to identify relatives with higher probabilities the simple bi-allelic SNPs
36
Characteristics of AISNPs
SNPs that collect key give a high probability of an individuals ancestry being from one part of the world or being derived from two or more areas of the world
37
Do SNP detection methods vary?
Yes- methods choice depends on depends on the application
38
Characteristics of PISNPs
SNPs that provide a high probability that the individual has particular phenotypes, such as a particular skin colour, hair colour, eye colour, etc
39
What’s direct sequencing?
PCR products are sequenced to reveal SNP sites
40
Whats TaqMan 5’ nuclear assay?
A fluorescent probe consisting of reporter and quencher dyes is added to a PCR reaction; amplification of a prob specific product causes cleavage of the probe and generates an increases in fluorescence
41
What’s Tm- shift
Allelic- specific PCR is performed with a GC-tail attactched to one of the forward allele-specific primers; amplified allele with GC-tailed primer will exhibit a melting curve at a high temperature
42
What is SNaPshot used for?
A detection of SNP variation using primer extensions
43
How are primers designed in SNaPshot?
They hybridise to specific alleles
44
Why do allele-specific primers have tails?
To separate the different sizes during electrophoresis
45
What type of nucleotides does SNaPshot use?
DdNPS are used but SNPs are under investigation
46
How are SNaPshot products separated?
By using electrophoresis
47
What does IRIS-Plex predict?
identification of eye colour (brown vs blue)
48
How can IRIS-Plex help in forensics?
Supports identification of a suspect
49
How does IRIS-Plex detect SNPs?
The primers hybridise to specific alleles ad separate through the use of tailed extension primers
Molecular Forensics
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