Forensic Bio - DNA Flashcards
What is DNA and where is it found in the body?
- deoxyribonucleic acid (genetic code of life)
- found in nucleus of all cells, except red blood cells
What is DNA composed of and what is the final structure?
- composed of a chain of nucleotides
- forms a double helix
What are chromosomes and how many does each human have? (autosomal and sex chromosomes)
- chromosomes are composed of DNA molecules
- humans have 23 pairs, 46 total
- 22 autosomal pairs, 1 pair sex chromosomes
Both chromosomes in a pair have the same ___ but different ____
genes, alleles
Define phenotype and genotype
phenotype = physical expression of genes genotype = genetic makeup
How many chromosomes are given by each parent?
23 from each parent
What is meiosis?
- process of halving, shuffling, and recombining of chromosomes that results in 4 unique cells with 23 chromosomes each
What is mitosis?
- When a unique sperm and unique egg form a unique zygote (contains genetic material from both parents), it undergoes division
What is cell differentiation?
- process in which cells obtain their specialized functions
What are short tandem repeats?
- 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
What is RFLP and its limitations?
- 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
What is PCR and its advantages?
Polymerase Chain Reaction advantages: - works with degraded DNA - only requires small amount of specimen - fast and inexpensive - easily stored in database
Why do PCR and STRs work well together?
- STRs can be amplified by PCR
- STRs are stable and less subject to degredation
- if too degraded can use mini-STRs
what does the STR Database contain?
- 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
Familial DNA
- used to find relatives of suspects
- affects probabilities because it increases the frequency of a profile
- identical twins cannot be differentiated with DNA
Y-Chromosome DNA
- uniparental inheritance (paternal lineage)
- Y-chromosome specific STRs for individualization
What 3 sections are in the National DNA Bank of Canada?
- 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
What DNA samples are kept in the Databank?
Samples are only added to the databank after conviction (everything else is destroyed)
- no medical or genetic details included
Why do most women have their DNA on file?
- Pap smear cells are sent for cancer research
- can be subpoenaed
Bill C-104
DNA sample can be collected under warrant
How can contamination affect DNA analysis and how can it be prevented?
- may magnify the wrong piece of DNA
- ensure scene security: bunny suits, double gloves, separate teams for related scenes
- lab security: separate scientists
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?
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)
