BI140 MANUAL

general requirements for a forensic biology application to be

accepted in the forensic field (SCIENTIFIC)

Using the three R's, having publications, and are there controls

general requirements for a forensic biology application to be

accepted in the forensic field (LEGAL)

scientific acceptance and judges discernment

Individual Characteristics

Unique to both the sample AND the reference sample (identical twins are exception)

Class Characteristics

Allow for sample to be grouped with other similar samples

Unknown (U) or Questioned (Q) sample

a sample with an unknown source

Known (K) reference sample

A sample whos source is known

Robust

Works under a variety of conditions/sample types

Reliable

Consistently produces results

Repeatable

Produces same resultes for the same sample

Molecules to Organisms

Molecules form Organelles → form Cells → form Tissues → form Organs → form Organisms.

What are enzymes and what do they do

Speeds up chemical reactions. Examples: DNA polymerase (Taq) synthesizes DNA; nucleases break DNA bonds.

What do enzymes end in

-ase (ex: DNA polyamerase)

Why is PPE worn?

protect investigators from exposure to the scene, and to prevent contamination of the evidence

How to collect dry stains (non absorbent surface)

moistened sterile cotton swab and then dry swab

How to collect dry stains (absorbent surface)

cutting

How to collect dry stains (surface that may inhibit DNA analysis)

Scraping into a druggist fold

FTA paper is used for what

Liquid blood/saliva reference samples; convenient to store samples for later data use

How to collect wet stain

dry sterile cotton swab

What is Locard exchange principle?

Cross transfer of evidence when physical contact is made with another object (AKA. “every contact leaves a trace”)

How to store dry evidence

package separately, in paper bags clearly labeled and sealed

How to store wet evidence

Air dry prior to collection.

How to store liquid evidence

sealed in plastic containers (NOT FROZEN)

How to store stained evidence

Not folded, if has to be folded, then place paper between the folds

Why would you take a control sample from a scene

can be used for elimination purposes or familial purposes to have a known reference to compare the samples to.

What is a chain of custody and what if it is broken

Chain of custody is documentation of who is in posession of what evidence and when. If broken, it can lead to evidence being thrown out due to possible tampering.

What is the structure of a DNA molecule

Double-stranded, antiparallel (5' to 3' and 3' to 5') helix with a sugar-phosphate backbone and base pairs: A pairs with T, G pairs with C.

What is nDNA & where is it found

Nuclear DNA. Linear, found in nucleus

What is mtDNA & where is it found

Mitochondrial DNA. Circular, found in mitochondria.

Cell theory

All living organisms are made from 1+ cells, all cells arise from other preexisting cells

Characteristics of human genome

23 chromosome pairs (22 autosome pairs + 1 sex pair), 3.2 billion base pairs

How is nDNA inhterited

50% from mom, 50% from dad.

How is mtDNA inherited

all inherited maternally

What is a gamete

sex cells; haploid

What are somatic cells

all other body cells except sex cells; diploid

What does diploid mean

Two sets of chromosomes

What does haploid mean

Single set of chromosomes (22 autosomes (non sex) and one sex)

What does homozygous mean

Has two identical alleles

What does heterozygous mean

Has two different alleles

Composition of blood

RBC (erythrocytes), WBC (leukocytes), Platelets (non cell: plasma)

What are alleles

different versions of each gene (A,T,G,C)

What blood cell types are used in forensics & how

White blood cells; contain nDNA. Only source of nDNA in blood

How do the characteristics of nuclear DNA (nDNA) impact forensic analysis?

Unique to an individual (individualizing), degrades faster.

How do the characteristics of mitochondrial DNA (mtDNA) impact forensic analysis?

Shared by maternal relatives, highly resistant to degradation.

How are red blood cells (erythrocytes) used in forensics, and what characteristic makes that possible?

Nulliploid (no nucleus/DNA); contain hemoglobin (heme) targeted by serological presumptive/confirmatory tests.

What are transcellular fluids and where is it found

Epithelial cells (ex: seminal fluid/vaginal secretion, buccal). Found in the cells within the fluids

What are Extracellular Nucleic Acids and where are they found

Nucleic Acids include DNA and RNA.

Layers of skin tissue (inner to outermost)

Subcutaneous layer, dermis, epidermis

which layer of skin is most likely to be left at the crime

scene

Cornified layer of the epidermis

What are the characteristics of the skin cells left at crime scenes in touch DNA samples, and how do they impact DNA analysis?

Shed cornified skin cells lack nuclei and organelles, resulting in very low DNA yields and a low profiling success rate (~12.4%).

Hair cycle

Anagen, catagen, telogen

What is anagen phase

Active growth. Best for DNA

What is catagen phase

When the bulb of the hair comes out; The end of the anagen phase, when cell death occurs.

What is telogen phase

The resting phase. Hair begins to shed and found at scenes. Only mtDNA.

Where is mtDNA found in hair

The hair shaft

Where is nDNA found in hair

the root/bulb structure

Osteocytes

“Bone cell”

Why are bone and teeth more likely to be left in older/degraded samples

Extracellular matrix of hydroxyapatite crystals preserves evidence. Harder tissues last longer

DNA is found where in bones

it is found in the osteocytes

What three main components make up a bone

Osteocyes, osteoblasts, osteoclasts

What is cortical (compact) bone?

Solid, dense outer layer.

What is the bone marrow cavity?

Inner hollow cavity filled with bone marrow.

What is the epiphysis?

Spongy (cancellous) bone at the ends of long bones.

What do cementoblasts

produce the cememtum

What type of DNA does cementum & cementoblasts contain

mtDNA & nDNA

What do odontoblasts do

produce dentin

What type of DNA does dentin contain

mtDNA (mitochondrial DNA)

Which sample types have high DNA profiling success rates (~86–92%), and why?

Semen & Blood (dense nucleated cells: sperm & WBCs).

Which sample types have moderate DNA profiling success rates (~37–73%), and why?

Cigarette butts, gum, saliva (shed nucleated buccal cells).

Which sample types have low DNA profiling success rates (~12–18%), and why?

Shed hair & Touch DNA (dead, anucleate, keratinized cells).

What is a presumptive test

indicates the possibility of a specific bodily fluid

What is a confirmatory test

Indication of extreme certanty the sample is that specific bodily fluid

Why is each presumptive test presumptive and not confirmatory?

They lack absolute specificity and can produce false positives due to the fluid reacting similarly with different subtances

What DNA does the pulp cavity contain

it contains nDNA

What do all of the presumptive blood tests detect, and how?

based on the oxidation-reduction reaction catalyzed by the heme moiety of hemoglobin

What type of tests are the confirmatory blood tests, and what do they detect?

Crystals of certain chemicals will form in the presence of heme molecules

Kastle-Meyer test

Presumptive, blood; detects heme and turns pink under alkaline (basic) conditions

What is the Leucomalachite Green (LMG) test

Presumptive, blood; detects heme and turns green under acidic conditions

Hemastix test

Presumptive, blood; detects heme and the strip turns from yellow to green

what is the Luminol test

Presumptive, blood; detects heme and emits light. Only visible in the dark and it fades, so photograph immediately

what is the Bluestar test

Presumptive, blood; detects heme and emits light. Works in diffused light and doesn't harm DNA

what is the Fluorescin test

Presumptive, blood; detects heme and fluoresces yellow-green under an ALS

What is ALS

Alternative light source

What is the Takayama (hemochromagen) test

Confirmatory, blood; detects heme and forms red crystals with pyridine and glucose

What is the Teichmann (hematin) test

Confirmatory, blood; detects heme and forms brown crystals with glacial acetic acid, salts, and heat. Best on aged stains

What can ALS on semen detect

Presumptive, semen; detects flavin and makes the stain fluoresce

What is the Acid Phosphatase / Fast Blue B test

Presumptive, semen; detects acid phosphatase and forms a purple precipitate

What is the Christmas Tree stain test

Confirmatory, semen; detects spermatozoa. Red head, green neck and tail.

What is the ABAcard PSA test

Confirmatory, semen; detects PSA and forms a band in the T zone. C band must appear too (pregnancy test-like)

What does ALS on saliva detect

Presumptive, saliva; detects amylase and makes the stain fluoresce

What does a Microscopic exam test for

Presumptive, saliva; detects buccal epithelial cells under magnification

What does Starch-iodine test for

Presumptive, saliva; detects amylase and the sample stays yellow. (looks for no reaction)

What does Phadebas test for

Presumptive, saliva; detects amylase and a blue color appears

What does RSID-Saliva test for

Confirmatory, saliva; detects human salivary alpha-amylase (HSA) and forms bands in both T and C zones

Which test gives brown crystals and works best on aged stains?

Teichmann

Which test gives red crystals?

Takayama

Which test is positive when the sample stays yellow?

Starch-iodine

Which blood test needs total darkness and fades?

Luminol

Which two tests use an immunochromatographic strip?

ABAcard PSA and RSID-Saliva