Cross prep for ev

Question 1

you didn’t collect these samples yourself, correct

Answer 1

• That’s correct
• I did not collect the samples
• They were collected, packaged, and sealed by police personnel before arriving at the laboratory
• My role began when I received the sealed items and verified the integrity of those seals

Question 2

you cant tell the court when the saliva was deposited on the straw, can you

Answer 2

• No, I cannot determine when the saliva was deposited
• DNA analysis can identify the profile of the contributor, but it cannot determine the exact time the biological material was left.

Question 3

is it possible that contamination occurred at the scene

Answer 3

• I cannot speak to what occurred at the scene
• What I can say is that when the exhibits arrived at the laboratory, the packaging was sealed, labelled, and showed no signs of tampering, and all laboratory procedures were performed according to standard contamination-prevention protocols.

Question 4

could contamination have happened in your lab

Answer 4

• Our laboratory follows strict contamination-prevention protocols, including physically separated work areas, personal protective equipment, and negative controls in each test
• No contamination was detected in any of the controls during my analysis

Question 5

what does 1 in 170 quadrillion really mean? isnt that an exaggeration

Answer 5

• No. That figure represents the statistical rarity of the DNA profile in the relevant population.
• It means that the chance of selecting an unrelated person with the same DNA profile is approximately 1 in 170 quadrillion.
• This number is produced through accepted population-genetics calculations used in forensic laboratories across Canada.

Question 6

could more than one persons dna be on the straw

Answer 6

The DNA profile from the straw (Q1) was a complete, single-source profile. There was no indication of multiple contributors in my results.

Question 7

could the dna have transferred second hand, like through touching something

Answer 7

• DNA transfer is always a theoretical possibility, but I cannot determine the mechanism of deposition
• What I can say is that the DNA recovered from the straw was a strong, single-source saliva profile, which is consistent with direct contact such as drinking.”

Question 8

you didnt test the gun or any other items in the diner, did you?

Answer 8

No, I only tested the two items that were assigned to me: the straw swab (Q1) and the victim’s reference sample (K1).

Question 9

what is your current job title

Answer 9

senior forensic DNA scientist at the centre of forensic science in toronto ON

Question 10

what level of evidence were you asked to work on

Answer 10

• the source level
• Who’s DNA was on that straw? The police can then decide what that means. I’m just looking at the DNA

Question 11

what type of forensic science do you work on

Answer 11

investigative

Question 12

do you understand your duty to the court

Answer 12

Yes. I understand my duty to be impartial, non-partisan, and serve the court.

Question 13

what is the difference between a biologist and a forensic biologist

Answer 13

• A biologist studies living organisms in general,
• while a forensic biologist applies biological principles specifically to analyze evidence in criminal investigations,
• such as DNA, blood, or other bodily fluids.

Question 14

what is the error rate for forensic bio

Answer 14

• according to a 2014 paper published in the Forensic Science International: Genetics
• While contamination and human error are general risks in forensic biology, they’re unlikely in this case.
• The evidence was handled under strict protocols, with proper contamination controls and chain-of-custody.
• My analysis followed accredited procedures, and there were no signs of error or contamination.

Question 15

why didnt you state an error rate in your paper

Answer 15

• it is not standard to include error rates for this line of forensic biology
• error rates are incredibly complicated to calculate, and thus are only formed when a distinct need is outlined
• this is not the case, there was no reason to expect any contamination

Question 16

how does a codis match work

Answer 16

• codis finds a hit
• this is linked to the unique identifier of the offender
• we then contact the lab that originally inputted their data
• they can then search their database and figure out who it is
• and let us know

Question 17

what is a chain of custody

Answer 17

a record that tracks possession
and control of evidence to ensure authenticity and integrity

Question 18

you stated the caucasian population stats, why?

Answer 18

• after codis gave us a potential match that I verified
• and we found out the identity of the individual, we knew his ethnicity was caucasian
• and thus the strength calculations were done w that database

Question 19

how was the specimen stored before/during analysis

Answer 19

• when we first got it it was in a fridge at 4C
• then after dna was taken out, stored in freezer at -20C
• this stops these proteins called nucleases from breaking down the dna

Question 20

describe the extraction process

Answer 20

• cells from the swab were dissolved and broken down by a chemical called a buffer
• so I had DNA and the rest of the cell, all mixed in together
• using this process called a qiagen spin-column, the DNA and rest of cell were separated
• then i took the dna out

Question 21

describe the quantitation step

Answer 21

• used a test called a qPCR
• it replicates the dna over and over and then comes to conclusions based on how it replicates
• it told me its not degraded auto/deg under 2
• was a male sample y present
• not a mixture y:auto ratio of 1:1

Question 22

describe how we know the samples werent degraded

Answer 22

• deg is a large amplicon near auto
• it should be a 1:1 ratio
• if its under 2 then not degraded

Question 23

what does ipc shift tell us

Answer 23

• should be less than .3
• it shows lack of pc inhibitors + enough sample dna

Question 24

describe the multiplex pcr step

Answer 24

• used a tool called powerplex 16
• allowed the small amounts of dna to be replicated over and over until we had a lot
• looked at specific standard regions of the dna that vary a lot from person to person

Question 25

describe the STR typing step + interpretation

Answer 25

- after we have a lot of the dna we want - theyre separated based on their size in a thing called gel electrophoresis - *reference material* - then a software called GeneMapperID compared these sizes to a reference ladder - thennn i come in to review - no flags. all allele assignments looked good

Question 26

how did you calculate the match probability

Answer 26

Used NIST 1036 US Population Dataset

Question 27

motivation to give evidence?? $$?

Answer 27

my duty is to be impartial, non-partisan, and to serve the court. i was hired by the crown, but i dont serve them.