Forensic Bio - DNA

Question 1

What is DNA and where is it found in the body?

Answer 1

• deoxyribonucleic acid (genetic code of life)

- found in nucleus of all cells, except red blood cells

Question 2

What is DNA composed of and what is the final structure?

Answer 2

• composed of a chain of nucleotides

- forms a double helix

Question 3

What are chromosomes and how many does each human have? (autosomal and sex chromosomes)

Answer 3

• chromosomes are composed of DNA molecules
• humans have 23 pairs, 46 total
• 22 autosomal pairs, 1 pair sex chromosomes

Question 4

Both chromosomes in a pair have the same ___ but different ____

Answer 4

genes, alleles

Question 5

Define phenotype and genotype

Answer 5

phenotype = physical expression of genes 
genotype = genetic makeup

Question 6

How many chromosomes are given by each parent?

Answer 6

23 from each parent

Question 7

What is meiosis?

Answer 7

• process of halving, shuffling, and recombining of chromosomes that results in 4 unique cells with 23 chromosomes each

Question 8

What is mitosis?

Answer 8

• When a unique sperm and unique egg form a unique zygote (contains genetic material from both parents), it undergoes division

Question 9

What is cell differentiation?

Answer 9

• process in which cells obtain their specialized functions

Question 10

What are short tandem repeats?

Answer 10

• nonsensical repetition of base pairs
• referred to as ‘junk’ DNA because most of it doesn’t code for anything
• sequence length varies person-to-person

Question 11

What is RFLP and its limitations?

Answer 11

• repeat sequences cut out of DNA using enzymes
• limitations: need high quality non degraded DNA, requires large amount of specimen, time consuming and expensive
• Restriction Fragment Length Polymorphisms

Question 12

What is PCR and its advantages?

Answer 12

Polymerase Chain Reaction
advantages:
- works with degraded DNA
- only requires small amount of specimen 
- fast and inexpensive 
- easily stored in database

Question 13

Why do PCR and STRs work well together?

Answer 13

• STRs can be amplified by PCR
• STRs are stable and less subject to degredation
• if too degraded can use mini-STRs

Question 14

what does the STR Database contain?

Answer 14

• the rarity of STR combos
• help determine statistical significance of a profile
• DOES NOT assign probability of guilt or that DNA came from suspect
• tells us the probability that it came from someone else is low

Question 15

Familial DNA

Answer 15

• used to find relatives of suspects
• affects probabilities because it increases the frequency of a profile
• identical twins cannot be differentiated with DNA

Question 16

Y-Chromosome DNA

Answer 16

• uniparental inheritance (paternal lineage)

- Y-chromosome specific STRs for individualization

Question 17

What 3 sections are in the National DNA Bank of Canada?

Answer 17

• Crime Scene Index: samples of DNA from unsolved crimes
• Convicted Offenders Index: samples from people who are incarcerated and convicted of sexual assault and murder
• Missing Persons Index: DNA from missing persons and found human remains

Question 18

What DNA samples are kept in the Databank?

Answer 18

Samples are only added to the databank after conviction (everything else is destroyed)
- no medical or genetic details included

Question 19

Why do most women have their DNA on file?

Answer 19

• Pap smear cells are sent for cancer research

- can be subpoenaed

Question 20

Bill C-104

Answer 20

DNA sample can be collected under warrant

Question 21

How can contamination affect DNA analysis and how can it be prevented?

Answer 21

• may magnify the wrong piece of DNA
• ensure scene security: bunny suits, double gloves, separate teams for related scenes
• lab security: separate scientists

Question 22

Compare and Contrast Nuclear and Mitochondrial DNA

inheritance, who passes it on?, who has it?, where is it found in the living and dead?, class/individual evidence?

Answer 22

Nuclear:
- generational (50% from each parent)
- passed on by everyone
- everyone has it
- sources in living: any nucleated cell (not red blood cells), saliva
sources in dead: fresh body - any nucleated cell, decomposed body - dentine
- individual evidence (unique due to recombination)

mtDNA

• maternal (100% from mother)
• passed on by mothers only
• everyone has it
• sources in living: any cell, hair shaft
• sources in dead: any cell, hair shaft
• class evidence (same throughout maternal line)