STR Analysis

Question 1

What is the main aim of DNA (STR) profiling?

Answer 1

To link a sample to a crime scene

Question 2

What samples are required for STR comparison?

Answer 2

DNA from the crime scene and a suspects known sample to compare it to

Question 3

What does a DNA match allow you to generate?

Answer 3

A match probability/ stats test

Question 4

What does exclusion mean in STR profiling?

Answer 4

No match

Question 5

What is done when no suspect is available?

Answer 5

Search the Q sample to whats already in the DNA database- arrest that person and take a sample from them

Question 6

What does inclusion mean?

Answer 6

It a match

Question 7

What do you do if it’s a match?

Answer 7

Report the statistical likelihood of the match occurring by chance by using the allele database frequencies

Question 8

Workflow for crime committed (11)

Answer 8

-Evidence (question) sample ‘Q’
-collection
-sample storage
-Characterisation
-Extraction
-Quantification
-Amplification
-STR markers
-Separation/ detection
-Data interpretation
-Stat interpretation

Question 9

Workflow for suspect developed (9)

Answer 9

-Reference sample ‘K’
-collection
-sample storage
-Extraction
-Quantification
-Amplification
-STR markers
-Separation/detection
-Data interpretation

Question 10

Inclusion and exclusion workflow

Answer 10

Database search <— Exclusion (no match) <— DNA profile comparison of Q and K —> inclusion (match) —>report with stats —>Plea/ court

Question 11

How was STR profiling developed?

Answer 11

In conjunction with DNA technology

Question 12

Why were early forensic DNA methods unsuitable for databases?

Answer 12

Not reproducible or standardised

Question 13

What does MLP stand for?

Answer 13

Multi locus probe

Question 14

What’s a MLP?

Answer 14

A probe that hybridizes to a number of different sites in the genome of an organism.

Question 15

Why were MLP systems difficult to use? (4)

Answer 15

-Issues with reproducibility
-they’re difficult to to interpret
-Require a high amount of molecular DNA
-No legal framework

Question 16

Why did MLPs fail for national DNA databases?

Answer 16

Results varied by lab as it’s not standardised