Forensics DNA study guide

What does DNA stand for?

Depxyribonucleic acid

All human cells contain DNA except

Red blood cells

___ of DNA is made of sugar (deoxyribose) and phosphate molecules

Backbone

Forming the middle of molecule made up of pairs of nucleotides or nitrogen bases

Rungs

What always pairs with Thymine (T)

Adenine (A)

What always pairs with Guanine (G)

Cytosine (C)

Cell organelles that store DNA

Chromosomes

How many chromosomes are in a body

46

Most males have __ and one __ sex chromosomes

XY

Most females have two __ chromosomes

XX

Who can give the Y chromosome

father

Segment of DNA that determines our traits

Gene

When genes come from different parents for the same trait they are referred to as

Alleles

What environmental factors can degrade DNA making it unusable

Heat, sunlight, moisture, bacteria, and mold

Is all the DNA found at a crime scene usable in a DNA profile?

No

What should NOT be packaged in airtight containers?

Bacteria, mold, and fungi, bag in paper, or well ventilated box

Remove blood with cotton swab moistened with distilled water

Cotton swab

What are you supposed to do with the cotton swab

Keep refrigerated and out of direct sunlight

Substrate control

Portion of unstained surface material

Cotton swab placed in subjects mouth and the inside of the cheek is vigorously swabbed transferring buccal cells to swab

Buccal swab

What does DNA have to be compared to?

DNA samples from victims and suspects

If individuals are not available what can DNA be obtained from?

Razor, hairbrush, toothbrush, cigarette butts, earplugs

How to minimize contamination of DNA evidence

Wear gloves, face mask, shoe coverings, change gloves, package each item in its own container

What does PCR generate

Multiple copies of DNA evidence

Variable numbers of tandem repeats

VNTR

Short tandem repeats

STR

XX

Female

XY

Male

Who determines the sex of the offspring?

Dad

How many pairs of chromosomes do humans have?

23 pairs

DNA collected from suspect

Buccal swab

RBC

No DNA

Why can’t DNA be used to solve every crime?

• not all DNA found at crime scene is usable on DNA profile

• Environmental factors (heat, sunlight, moisture, bacteria, and mold) can degrade DNA making it unusable

• DNA testing cannot identify WHEN a suspect was at a crime scene or for HOW LONG

How can DNA be used as evidence?

• DNA can identify a victim through DNA from relatives even when no body can be found

• DNA can link crime scenes by linking the same perpetrator to different scenes locally, statewide, or nationally

• DNA can place an individual at the crime scene, in a home or in a room, where he claimed not to be

• DNA collected from crime scene can link a suspect to the evidence or eliminate them as a suspect