Name
TEACHER COPY
Period _______ Date ______________
Forensic Science
Chapter 7 – DNA FINGERPRINTING
Directions: Fill in the information from the Classroom Chart or the Online Chart.
Forensic Science Standard and element:
SFS3. Students will analyze the use of toxicology, serology, and DNA technology in forensic investigations.
f.)
Compare short tandem repeat patterns (STR) and relate to identifying the DNA of an individual.
g.)
Explain the use of the DNA database for DNA profiling.
1.) Put chart in Science Notebook behind the Charts section
after it has been checked.
2.) All parts were accurate and complete with no abbreviations.
3.) Handwriting was neat.
4.) Information was dark enough to be easily read, and chart was neat.
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(Part of Notebook Grade)
HISTORY OF BIOLOGICAL EVIDENCE IN FORENSICS
Most laboratory techniques used in forensics were originally developed for other purposes
such as for medical diagnosis and medical treatments.
1. In September 1984, Dr. Alec Jeffreys, a geneticist from the University of Leicester in Great
Britain was studying hereditary diseases in families. He was focusing on methods to resolve
paternity and immigration disputes by demonstrating the genetic links between individuals.
He was asked to help in a murder case and used his process that he called genetic
fingerprinting to convict Colin Pitchfork of the murder and rape of three young girls. This
was the first time DNA fingerprinting was used to solve a crime.
2.
3. DNA fingerprinting is also known as DNA profiling or genetic fingerprinting.
THE FUNCTION AND STRUCTURE OF DNA
DNA is deoxyribonucleic acid, a self-replicating material present in nearly all living
organisms as the main constituent of chromosomes. It is the carrier of genetic information.
Chromosomes contain the recipe for making a living thing. They are found in almost every
cell’s nucleus and are made from strands of DNA (deoxyribonucleic acid). Segments of DNA
called "genes" are the ingredients. Each gene adds a specific protein to the recipe. Proteins
build, regulate and maintain your body. For instance, they build bones, enable muscles to
move, control digestion, and keep your heart beating.
o
o
Nitrogenous Bases—pairs of molecules that form the rungs of the DNA “ladder”
Four types of Bases
• A (adenine)
• C (cytosine)
• G (guanine)
• T (thymine
o Base-Pairing Rules
• Adenine (A) binds only with thymine(T)
• Cytosine (C) binds only with guanine (G)
SNP - single
nucleotide
polymorphism
s
To summarize, your genes are located on your chromosomes. You have two versions of
each chromosome (23 pairs giving you 46 total), so each of your alleles for a trait is found
on one of a pair of corresponding chromosomes.
In females, the sex chromosomes are the 2 X chromosomes. Males have one X chromosome and
one Y chromosome. The presence of the Y chromosome produces a boy.
DNA IDENTIFICATION
Polymorphism is the presence of genetic variation within a population, upon which natural
selection can operate. It is common in nature.
Examples include:
o the separation of most higher organisms into male and female sexes
o different blood types in humans
DNA Fingerprinting (Profiling) isolates and analyzes polymorphisms
DNA fingerprints appear as a pattern of bands on X-ray film.
99.9% of human DNA sequences are the same for everyone, but some are different enough
to tell one person from another. DNA fingerprinting uses repetitive sequences that are
highly variable. There are 13 distinctly different markers for every person.
The human genome is composed of over 3 billion base pairs of information organized into
23 chromosomes.
DNA PROFILE
Two types of repeating DNA sequences
o Variable Numbers of Tandem Repeats (VNTR)
• The number of repeats varies from person to person
• 9 to 80 bases in length
o Short Tandem Repeats (STR)
• 2 to 5 bases in length
• Shorter lengths make STRs easier to use than VNTRs
o VNTR and STR data are analyzed for
• tissue matching
• inheritance matching
o Tissue Matching
• Two samples that have the same band pattern are from the same person
o Inheritance Matching
• Each band in a child’s NDA fingerprint must be present in at least one parent
DNA POPULATION DATABASES
o Population genetics:
• the study of gene variations among groups of individuals
• Analyze the probability of a random person with the same alternative form of a
gene (an allele)
o Examples
• Identifying the suspect in a crime
• Identifying an alleged father in a paternity case
SOURCES OF DNA
o Biological evidence: examples include saliva, blood, skin, hair, seminal fluid
o Individual evidence is capable of identifying a specific person.
o Small amounts may be only trace evidence
o Polymerase chain reaction (PCR) technique generates multiple copies of DNA evidence
PREPARING DNA SAMPLES FOR FINGERPRINTING
DNA is mixed with special enzymes
• Enzymes cut apart the DNA in specific places forming different sized fragments
• DNA is separated within an agarose gel
• An electric current is passed through the gel separating the fragments by size
Extraction
1. Cells are isolated from biological evidence such as blood, saliva, urine, semen, and
hair
2. The cells are disrupted to release the DNA from proteins and other cell components
3. The DNA can be extracted from the cell nucleus
Amplification
o VNTR analyses—polymerase chain reaction (PCR) can be used to amplify the DNA
that contains the VNTRs
o STR profiles—restriction enzymes are unnecessary; PCR allows the amplification of
the strands with STR sequences
Gel electrophoresis is a technique used to separate mixtures like DNA and proteins. The
separation is based on how positively or how negatively charged a molecule is and its size.
Gel electrophoresis uses a gel (like gelatin) and the application of an electric field through
the gel.
o DNA samples are placed in gels through which electronic currents are passed
o DNA fragments line up in bands along the length of each gel
o
PROBES
o DNA probes
• identify the unique sequences in a person’s DNA
• are made up of different synthetic sequences of DNA bases complimentary to
the DNA strand
• bind to complimentary bases in the strand (see the fragmentary DNA bands
above)
o In most criminal cases, 6 to 8 probes are used
ANALYSIS OF DNA FINGERPRINTS AND APPLICATIONS
Bands and widths are significant in
matching samples of DNA
o
DNA fingerprinting can
• match crime scene DNA with a suspect
• determine maternity, paternity, or match to another relative
• eliminate a suspect
• free a falsely imprisoned individual
• identify human remains