Forensics
DNA SCIENCE
What We Will Study
OPatterns of Inheritance
OThe Molecule DNA
(deoxyribonucleic acid)
ODNA’s use in Forensics
OWho Dunnit (DNA Lab)
Patterns Of Inheritance
O All living things possess physical and behavioral
characteristics called traits.
*Hair Color
*Taste
*How Fast a Person Angers
O Each trait is inherited from an
organism’s ancestors.
O The trait moves from one organism to
another via a piece of DNA called a
gene.
O Genes are passed down from
generation to generation through the
reproductive process.
O Organisms that are created through
sexual reproduction have two parents so it
would stand to reason they have at least
two different genes for each trait.
O Because each organism has many
thousands of different genes, and there
are two parents organisms, that means
each new organism is unique. (It contains
its own unique DNA pattern.)
Facts
O DNA comes in packages called Chromosomes
O Different organisms have different numbers of
chromosomes.
O Humans have 23 pair of chromosomes.
O 23 come from the biological father
O 23 come from the biological mother
O This means you have 2 number one
chromosomes, 2 number two
chromosomes etc.
O All human DNA is 99.9% identical.
O It is the 0.1% that makes us all
different.
O No two humans have the same DNA
unless they are identical twins
Review
1. List five traits you have.
2. How many genes do you have for each
trait?
3. Where did you get these genes?
4. A gene is a piece of ____.
5. DNA come in packages called ______.
6. Humans have 23 pairs of _______.
7. The letters DNA stand for _____ ____ ____
8. How much of your DNA is unique to you?
9. Can identical twins have identical DNA?
O DNA is constructed into a code for all of an
organism’s traits.
O There is a certain code for red hair.
O There is a certain code for eye color
O There is even a certain code for finger
length. (Compare the length of your pointer
finger compared to the length of your ring
finger. Which is longer? Check with your
classmates to see if they all have the same
results.)
O Traits come from parts of DNA called
“Genes”.
O Genes are simple stretches of DNA
that code for a particular
characteristic, (trait).
O On one strand of DNA there may be
thousands of genes.
O 5% of human DNA is made of genes.
O Genes even code for things that are not easy to
see like mathematical ability and quality of
memory.
O To Summarize:
DNA
Genes
Chromosomes
Chromosomes
O Each individual chromosome is made of gigantic,
long strings of DNA. The DNA is wound around
proteins and in the end takes the shape of an “X”.
O A housefly has 8 chromosomes and a corn plant has
20.
O Abnormal numbers of chromosomes in an individual
organism causes major biological problems.
O All genetic information is passed from
generation to generation through
chromosomes.
O Chromosomes contain two types of DNA
O Coding DNA – this DNA makes up genes.
O Non-Coding or Junk DNA – this is
non-genic DNA
O Both types of DNA are very useful in a
scientific sense
O It is the information in chromosomes
that make them useful in forensics.
Since no two people have the same
DNA, any blood or bodily fluids left at a
crime scene provide an identification
tag .
O DNA information is so powerful that
trial juries give DNA evidence a
tremendous amount of weight in their
decision making.
DNA (The Molecule)
O The DNA molecule was first defined in the
1960s by two scientists, James Watson and
Francis Crick. (Crick was British and Watson
an American)
O It is one of the most important discoveries in
human history and they won a Nobel prize
for their efforts.
O They found that the molecule is actually shaped
like a right-hand twisted ladder, helix, or spiral.
Review…
1.
2.
3.
4.
5.
Explain what chromosomes are made up
of.
Draw the general shape of DNA and
identify where the proteins are.
Explain the two types of DNA and their
purposes.
Who and when was DNA first
discovered.
What year was DNA first used in a
criminal case?
O The ladder is made from four different
molecules called “nucleotides”.
O Each nucleotide is made of three
parts.
O Phosphate
O Pentose, (5 sided) sugar
O One of four nitrogenous bases.
phosphate
Pentose
Sugar
Nitrogenous
Base
O What makes one of the four nucleotides
different from the next is the nitrogenous
base it possesses.
O The four bases are as follows:
O Adenine
O Cytosine
O Guanine
O Thymine
phosphate
Pentose
Sugar
Adenine
phosphate
Cytosine
Pentose
Sugar
phosphate
Guanine
Pentose
Sugar
phosphate
Thymine
Pentose
Sugar
O As the molecule assembles itself, it
does so in a 2 sided fashion.
O Watson and Crick found that when
they looked at the nucleotides, one
thing was obvious.
O The nucleotide adenine was
ALWAYS bonded to the nucleotide
thymine and cytosine was always
bonded to guanine.
O Not only is adenine always bonded to
thymine, it is bonded with 2 hydrogen bonds
O
P
P
S
Adenine
Thymine
S
O Not only is cytosine always bonded to
guanine, it is bonded with 3 hydrogen bonds
O
P
P
S
cytosine
guanine
S
Review…
1. Explain the shape of a DNA molecule.
2. Identify the three parts of a nucleotide.
3. Show how these 3 parts are connected to each
4.
5.
6.
7.
other.
What are the four nitrogenous bases in DNA?
Which bases bond to which bases?
What type of bond is between the pairs of bases?
Identify which base pairs have double bonds and
which have triple bonds.
O Not only is the DNA shaped like a ladder, the ladder
actually twists as shown below.
BACKBONE
CYTOSINE
THYMINE
GUANINE
N BONDS
ADENINE
Fill in the other side of the
DNA Molecule.
O Fill in the matching nucleotides and include the
hydrogen bonding.
O A C
G
C T C A
A G C
T A C
C T
A T
C
Functions of DNA
O DNA:
O Stores and passes genetic
information from generation to
generation.
O Runs all cellular activity.
O Changes (undergoes
mutation)
O AACTCTGGGCAAATCGATCCG
O AACTCTGCGCAATTCGAGCGC
O As you can see, there are only a few
nucleotides that are different. BUT these
few different nucleotides cause changes in
eye color, height. Intelligence, - all kinds of
things
How is DNA used as evidence?
• Each person’s DNA is different from other people (except identical
twins).
• DNA collected from a crime scene can either link a suspect to the
evidence or eliminate a suspect, similar to the use of fingerprints.
• DNA can identify a victim through DNA from relatives, even when
no body can be found.
• DNA can link crime scenes together by linking the same perpetrator
to different scenes locally, statewide, and across the nation.
• DNA can place an individual at a crime scene, in a
home, or in a room where the suspect claimed not to
have been.
• DNA can refute a claim of self-defense and put a
weapon in the suspect's hand.
• It can change a story from an alibi to one of consent.
DNA Strand Image & information : http://www.dna.gov/audiences/investigators/know/
What factors affect DNA evidence?
Several factors can affect the DNA left at a crime scene, such as
environmental factors (e.g., heat, sunlight, moisture, bacteria, and mold).
Therefore, not all DNA evidence will result in a usable DNA profile.
Further, DNA testing cannot identify when the suspect was at the crime
scene or for how long.
What is CODIS?
CODIS stands for COmbined DNA Index System, which is an
electronic database of DNA profiles that can identify suspects. DNA
profiles from individuals convicted of certain crimes, such as rape,
murder, and child abuse, are entered into CODIS and help officers
identify possible suspects when no prior suspect existed.
Did you know?
Each human cell contains three billion DNA
base pairs. Our unique DNA amounts to 0.1%
or 3 million base pairs.
DNA information : http://www.dna.gov/audiences/investigators/know/
REVIEW….
1.Name 6 ways DNA is used as
evidence.
2.What factors affect DNA evidence?
3.How long can DNA sample be
reliable?
4.When was the first DNA evidence
used in a court case?
5.Write what CODIS stands for and
explain what it is.
C. Identical or not?
A. Who done it?
Which sets of twins are
identical twins?
Which suspect matches
the bloodstain?
B. Whose your daddy?
Which sample is most
likely to be the father?
F1 or F2
Information & image from http://www.teachersdomain.org/resource/tdc02.sci.life.gen.lp_dnamysteries/
True or False?
Which three statements below are true?
1. The DNA in a man's blood is the same as the DNA in his skin cells and
saliva.
2. Each person's DNA is different from every other individual's.
3. DNA can be found in all the cells in our bodies except the blood cells.
4. DNA can have forensic value even if it is decades old.
5. DNA evidence was first used to get a conviction in a trial in 1987.
Watch the video segment from NOVA: "The Killer's Trail" and
be ready to answer the questions on the next slide.
Video available at Nova_Killer Trail.zip
More information available at http://www.pbs.org/wgbh/nova/sheppard/
Video Quiz
Choose the best answer for each.
1. Who was the victim?
A. Marilyn Sheppard
B. Sam Sheppard
C. Sam Sheppard, Jr.
2. What are the keys to DNA fingerprinting?
A. Chromosomes
B. Alleles
C. Nitrogen bases
3. Where did the scientist get the sample of DNA for Marilyn Sheppard?
A. Hair
B. Skin
C. Fingernail
4. Whose blood was found in the blood trail?
A. Marilyn Sheppard
B. Sam Sheppard
C. Neither
Secret of Photo 51
Fill in the worksheet:
O https://www.youtube.com/watch?v=0tmNf6
ec2kU
Review
1. List five traits you have.
2. How many genes do you have for each
trait?
3. Where did you get these genes?
4. A gene is a piece of ____.
5. How much of DNA is made up of gene?
6. DNA come in packages called ______.
7. Humans have 23 pairs of _______.
8. The letters DNA stand for _____ ____ ____
9. How much of your DNA is unique to you?
10.Can identical twins have identical DNA?
Review…
1.
2.
3.
4.
5.
Explain what chromosomes are made up
of.
Draw & describe the general shape of
DNA and identify where the proteins are.
Explain the two types of DNA and their
purposes.
Who and when was DNA first
discovered.
What year was DNA first used in a
criminal case?
Review…
1. Explain the shape of a DNA molecule.
2. Identify the three parts of a nucleotide.
3. Show how these 3 parts are connected to each
4.
5.
6.
7.
other.
What are the four nitrogenous bases in DNA?
Which bases bond to which bases?
What type of bond is between the pairs of bases?
Identify which base pairs have double bonds and
which have triple bonds.
DNA Replication LT2
Functions of DNA
O DNA:
O Stores and passes genetic
information from generation to
generation.
O Runs all cellular activity.
O Changes (undergoes
mutation)
DNA REPLICATION
O DNA passes genetic information from generation
to generation. It manages this by going through a
process called DNA Replication.
O Replication occurs just before the Cell containing
the DNA splits into 2 new cells. (Remember –
every cell has to have the right amount of ‘DNA of
there will be problems.)
O Human cells have 46 chromosomes. Just before a
cell divides into two cells it makes a copy of its
DNA, (92 chromosomes). It divides into two new
cells, each with 46 chromosomes.
O https://www.youtube.com/watch?v=8kK2zwjRV0
M
O Replicating DNA is not hard to understand. There
O
O
O
O
O
are only 5 easy steps
1. Unwind the DNA ladder. (Enzyme)
2. Unzip the DNA Molecule. (Enzyme)
3. Complementary Base pair the nucleotides.
(Enzyme)
4. Rezip the new molecule. (Enzyme)
5. Rewind the new molecules. (Enzyme)
O Step 1
O A protein called an enzyme unwinds the DNA.
O It was a twisted ladder – now it is just a ladder
O Step 2
O Another enzyme unzips the DNA at a particular
point.
O Step 3 Complimentary Base Pairing
O Now that the DNA is open,
nucleotides, always present in the
cell, complimentary base pair to their
partners.
O Adenines bond to thymines
O Cytosines bond to Guanines
O This DNA has been unwound and unzipped.
A
C
T
G
A
C
A
T
G
A
C
T
G
T
O Complementary nucleotides come in and match up
with their partners.
A
CG
T A
G C
A T
C G
A T
T A T
CG
T A
G C
A T
C G
A T
O Now the new nucleotides are joined together to for
a new strand of DNA
A
CG
T A
G C
A T
C G
A T
T A T
CG
T A
G C
A T
C G
A T
O Step 4
O Once the new nucleotides have lined up
correctly, (As with Ts and Cs with Gs), an
enzyme joins the sides together to make
two exact DNA molecules.
O Step 5
O The 2 new molecules rewind into normal
twisted ladder shapes….
O Now that the molecule has been copied, the cell
can divide in two and each new cell will have an
EXACT copy of the original cells DNA.
O This is important. It guarantees genetic
consistency.
O Damaged skin cells will be replaced with skin cells.
O Humans will always give birth to humans.
O So now we know that humans possess 23 pair of
chromosomes and 99.9% of human DNA is
identical. This being the case – why do we look so
different?
O What makes us different is the order of the DNA
base pairs in that .1% of DNA that is different.
O In a particular gene, one person will have this
order of base pairs.
AACTCTGGGCAAATCGATCCG
Another person may have the following order.
AACTCTGCGCAATTCGAGCGC
Use of DNA Replication in Anthropology…
Ancient DNA - Bringing the Past to Life:
https://www.youtube.com/watch?v=F-pcdy2zsl4
Review…
• Name 3 functions of DNA.
• DNA passes genetic information
from generation to generation.
It manages this by going through
a process called__________.
• List the 5 steps in this process.