forensics Unit 2

DNA is a

nucleic acid

Where is DNA found

in nucleus or mitochondria

How many chromosomes do MOSt human cells have

46 total chromosomes

23 pairs

What is the role of genes

control the traits of the organisms, and therefore can vary between individuals

What shape is a strand of DNA

double helix

What are the components of DNA? 

sides of helix= backbone of DNA made up of alternative sugar + phosphate molecules 

• sugar= deoxyribose 

How is the double helix formed?

base pairings of two sugar phosphate backbones bind together

What are the 4 nitrogen bases? what are their pairs?

Adenine, Thymine, Guanine and Cytosine

• help code DNA with instructions for cells

• A-T and C-G

Whats the role of the genome?

Genome= total amount of DNA in all; codes the blueprint for the human body + hpw it works, tells the body to make proteins + other needed molecules 

• in both nucleus and the mitochondria

• 3 billion base pairs 

Which Segment contain unique patterns?

polymorphisms, non coded DNA segments, unique patterns of repeated base sequences that are unique to individuals

Variable numbers of tandem vs short tandem?

• VNTR: 9-80 base length

• STR: 2-5 base length

Exons

encoded DNA with directions to build molecules

Introns

are undcoded DNA, that do not code for production of nucleus

What is the purpose of DNA fingerprinting? In what ways was it used

to distinguish between individuals of the same species by using samples of DNA

• links suspects to crimes, identify body of killers

Whats the source of DNA fingerprinting? Examples?

Trace evidence; biological evidence left at crime scenes

• ex: saliva, blood, semen, skin,hair roots, body tissue, cells, urine. 

Steps to DNA fingerprinting?

1. extraction of DNA

2. cutting the DNA into restriction fragments 

• RFLPs, Restriction Fragment Length POlymorphisms

3. Amplifications (making copies of those fragments) 

• use PCR 

4. Electrophoresis: a process that separates RFLPs accurately to their length creating a DNA fingerprint. 

How is DNA separated and purified?

1. Cells broken down to release DNA 

• if only small DNA, can go to amplify with PCR

2. DNA cut fragments with restriction enzymes, cut DNA at base pair sequences

• many different sizes 

3. Fragments separated on the side using  gel electrophoresis 

• injected into wells 

4. Patterns of fragments distributed then analyzed

What is main function of PCR?

make thousands of copies of DNA that investigators want to analyze

What are the 3 steps of PCR?

Denaturation, annealing, elongation

Annealing

spontaneous pairing of complementary DNA or RNA sequences by hydrogen bonding to create a double stranded molecule. 

Extension

Using the loosened nucleotides of each base to grow the complementary DNA strand. The end result is two double stranded production of DNA 

Restriction Enzymes are used in what step of DNA profiling

Step 2

What do restriction enzymes do? How does this benefit the process?

thet cut DNA out a specific base sequence.

• allows for the precise manipulation, cutting, and reassembly of DNA for processes like gene cloning, genetic engineering, and creating DNA fingerprints for forensic analysis.

• enables scientists to isolate specific genes, insert them into vectors, and build new DNA molecules with desired traits. 

What do restriction enzymes create?

restriction fragments

• all different sizes because the base sequence being cut may be far apart (long fragment) or close together (short fragments) 

Parts of a tooth

• enamel 

• dentin 

• gums 

• bone

• pulp 

What are the parts of a tooth made of? 

Calcium and phosphorus, or enamel and dentin 

(Children) - How many primary and permanent teeth

20 primary

32 permanent

Collecting Bite mark evidence

photographed asap while impressions are visible 

• bite marks swabbed for saliva, could have DNA 

• different sizes: affects jaw, each unique

individualizing factors include:

• Dental work (fillings, crowns, caps)

• Damage (chips and cracks)

• Coloration

• Distances between teeth

• Alignment of teeth

• Dimensions of each tooth

• Arch of the roof of the mouth

crossbite 

One or more of the upper teeth biting on the inside of the lower teeth characterizes a crossbite.

• occur in the front and/or the sides of the mouth.

Underbite 

The lower teeth biting in front of the upper teeth characterizes an underbite.

• caused by undergrowth of the upper jaw, overgrowth of the lower jaw, or a combination of the two

• or caused by tipped back upper incisors, flared lower incisors, missing upper teeth, or a combination of all.

Open Bite

• Inadequate vertical overlap of the front teeth characterizes an open bite.

• caused by oral habits such as tongue thrust, digit sucking, or jaws that don’t grow evenly.

Overbite (deep bite)

a measure of the vertical overlap of the upper and lower front teeth.

• Excessive overbite may be caused by disproportionate eruption of front teeth or overdevelopment of the bone that supports the teeth.

Where can glass be found in a crime scene?

breaks ins, car shootings, car accidents etc.

primary ingredients

Silicone dioxide (SiO2) or Silica

Types of Glass

1. Soda Lime Glass: Sodium + calcium oxide (CaO) aka lime.

• most common, inexpensive and easy to melt and shape, relatively strong

• used for windowpanes, glass containers, drinks

2. Crystal or Leaded Glass: Calcium Oxide of other glasses is replaced with lead oxide (PbO)

• denser which causes sparkle as light passes through

3. Pyrex: used in ovenware and laboratory glassware; able to withstand wide range of temperatures.

• kitchen staple

Properties of glass 

distinguish difference with density, each glass has density specific to that glass 

• to find density, divide mass (g) by volume (mL)

• Mass found by using a balance 

• Volume found by water displacement in a graduated cylinder. 

Fractures:

The side where the impact takes place, the glass surface is compressed or squeezed together.

• The other side of the glass (side away from the impact) stretches and is under tension and develops fractures.

• glass is flexible, but when not able to stretch, it cracks and can break

PROVIDES CLUES: about direction and rate of impact.

How Glass used as evidence

provide clues about direction and rate of impact

glass as evidence:

• photograph and identify glass b4 moving

• all glass collected bc more than one type could be present and physical matches might be made

• Identify and mark inside and outside of the glass

• small glass= paper bibles, pill boxes etc

• large glass= boxed, separate with cotton

Impressions

objects or materials that have retained the characteristics of other objects through direct contact

• created when one object is pressed against another material with enough force to leave an impression of the object 

• ex: shoeprints, tool marks, tire tracks, bite marks and marks on fired bullet 

• ex: sole: pattern on bottom footwear 

quality of impression depends on object + surface making the impression (how hard +soft material is, like osil mud, dust, concrete, grass, skin etc.) 

Types of impressions

Patent, Latent or Plastic

Patent impressions

car travels over a liquid such as paint, blood or tar. 

Latent impressions

deposited from the oil used to soften tires

Plastic Impressions

made when vehicle drives on mud, sand or snow

Impression evidence

detectives can gain info about:

• the number of people at scene

• movement of individuals at crime scene

• entrance and exit to the scene

ex: shoemarks, tire marks, tire tracks, bite marks, marks on fired bullet, dental impressions, sole of shoe

What do shoe databases contain?

tread patterns used by different manufacturers, and can often be traced down to retailers which sell the shoe.

how can you highlight 3D impressions

spray pain or spruaing with colored wax spray

Dusting (used to lift latent impressions)

similar for dusting fingerprints

• fingerprint powder can visualize print

• lifted with adhesive or gelatin

• photographed for evidence

materials used to cast plastic impressions 3-D

Dental stone: fills in the print and produces a cast

how do we use forensic photography 

oblique, ultraviolet, infrared or other special methods 

photographs are taken for later comparison with suspected footwear, therefore they must be very clear 

quality photographs taken of impressions if they can’t be transported 

• to enhance impressions 

Electrostatic lifting

a charge is used to lift dry materials from surface to black film to recover impression

• normally on tile, wood, etc

• lift provides more contrast, on-destructive

• photographed for evidence

what chemicals used to enhance shoe prints?

reagents like leuco crystal violet, amido 10 black, or fuchsin acid may be used

What info can we gain from footwear impressions

• Identification of Footwear

• Elimination of Footwear

• Participation of suspect in crime

• Location of Impressions

• Rebuttal or confirmation of alibis

• Determination of shoe brand - FBI Laboratory

• Quality photographs should be taken of impressions if they can not be transported

• Photographs are taken for later comparison with suspected footwear; therefore they must be very clear

• Scale should be used to gauge size of footprint

Gait

the pattern of how you walk

factors affect gait

age, gender, height, size + shape of being components, distribution of mass in body segments, join mobility, muscle strength, type of clothing + footwear, habit, psychological status

tire groove 

a depression in the tread of pattern 

tire rib

ridge running down the tread area around the circumference of the tire

tire ridge

elevated area on the tread pattern (everything thats not groove) 

radial vs bias tire

most passenger tires today= radial-ply tires

some bias tires are made and can be found on older vehicles

• tires made from various compounds of unvulcanized rubber, steel, and fabric.

• tread and sidewall patterns are molded into a green tire

track width 

distance from the center of the tread pattern on the left tire ot the center of the read pattern on the corresponding right tire

• help identify vehicle + check in database

wheel base

distance from the center of the front axle on vehicle to the center of the rear

• measurement of the center of hubs of front wheels to center of hubs of rear wheel

• normally not present at crime scenes, unless the tracks show evidence of being parked

turning diameter

measure of how tight a circle can be driven by a vehicle

• pertains to front wheels only 

• smaller case= smaller turning diameter

formula for calculating= (B²/A) +A 

• B= distance between two points (x and x’) on turn circle 

• A= distance between outer margin and a mid point, between x and x’ 

skid marks

form when diver slams brakes suddenly 

• show distance the vehicle traveled after the brakes were applied 

• help calculate speed of vehicle 

yaw marks 

sideways skid marks, produced when vehicle turns faster than it can handle 

• accompanied by smoke and squealing sounds 

tire scrubs

damage to tires can show the area of impact

tread pattern

tire treads= ridges and grooves that channel water away from the wheel and provide traction for the vehicle

the unique design of a tires surface

noise treatment

arrangement of design elements used to reduce tire noise