DNA
(or more formally: Deoxyribonucleic
Acid)
By Caitlin and Audrey
Basic Information
• DNA is a double helix formed by base
pairs attached to a polymer (sugarphosphate) backbone.
• Most DNA is located in the cell nucleus
(but a small amount of DNA can also be
found in the mitochondria)
• The information in DNA is stored as a
code made up of four chemical bases:
Adenine (A),
Guanine (G),
Cytosine (C),
Thymine (T).
Fun Fact
Human DNA consists of about 3 billion bases,
and more than 99 percent of those bases are
the same in all people. The order, or
sequence, of these bases determines the
information available for building and
maintaining an organism, similar to the way
in which letters of the alphabet appear in a
certain order to form words and sentences.
Basic Information Continued
 DNA bases pair up with each
other, A with T and C with G, to
form units called base pairs.
Each base is also attached to a
sugar molecule (the long swirly
strands) to make the double
helix structure
Making Proteins
Most genes contain the information needed to
make functional molecules called proteins.
STEP 1: Transcription. In this process, the The journey from gene to protein is complex
and tightly controlled within each cell. It
information stored in a gene’s DNA is
transferred to a similar molecule
consists of two major steps: transcription and
called RNA (ribonucleic acid). The type translation. Together, transcription and
of RNA that contains the information
translation are known as gene expression.
for making a protein is called
messenger RNA (mRNA) because it
carries the information, or message,
from the DNA out of the nucleus into
the cytoplasm.
STEP 2: Translation is getting from a gene
to a protein, and this takes place in
the cytoplasm. The mRNA interacts
with a ribosome, which “reads” the
sequence of mRNA bases. Each
sequence of three bases, called a
codon, usually codes for one particular
amino acid. (Amino acids are the
building blocks of proteins.) A type of
RNA called transfer RNA (tRNA)
assembles the protein, one amino acid
at a time.
The RNA opens DNA
to copy the DNA’s
information, acting
like a zipper. Then
once transported to
the cytoplasm, in
the Ribosome, the
tRNA assembles the
protein one amino
acid at at time.
Genetics Example: Skin Color
Scientists have figured out that several genes are involved in skin color.
1. One of these genes is the melanocortin 1 receptor (MC1R). When MC1R is
working well, it converts pheomelanin* into eumelanin*. If it’s not working
well, then pheomelanin builds up, resulting in freckles.
*Eumelanin is black or brown pigment and pheomelanin is red or yellow pigment.
Two other skin color genes were first identified in fish.
2. Researchers studying the stickleback fish found that the kit ligand gene (kitlg)
was different between dark and light stickleback fish. They also found that
humans have different versions of this gene too and that certain versions lead
to lighter skin. The kit ligand gene is needed for the survival of melanocytes.
So if a person (or a fish) has a version of this gene that doesn’t work well,
their melanocytes won’t survive as well. Fewer melanocytes will mean less
pigment. And so lighter skin.
Fun Fact: Scientists have figured out that lighter skinned East Asians get their
skin color mostly from a non-working version of kitlg.
Genetics Example: Skin Color Continued
3. Researchers studying zebrafish with light colored stripes
found another gene involved in human skin color,
SLC24A5. The fish with light colored stripes had a
version of this gene that didn’t work well. When they
looked in people, researchers found that some lighter
skinned people also had a poorly working version of this
gene.
Fun Fact: Northern European people with lighter skin
often have a poorly working version of SLC24A5.
These are just some of the genes that researches know of
that effect skin color. More than likely, a ton more exist.
This serves as one example of how DNA’s sequence of
base pairs play out in our traits.
Punnett Square
it is a diagram that illustrates the
prediction of the outcome of a
cross
it is named after Reginald Punnett,
the creator of the method
it is most commonly used to
determine or predict the
probability of producing offspring
of a particular genotype
Punnett Square Continued
There are two types of Punnett Squares:
Monohybrid Cross
Dihybrid Cross
DNA Deformities
 When the RNA does not copy correctly, deformities can
occur
 Example: 1p36 Syndrome
A congential genetic disorder or deformity that
 Is characterized by intellectual disability
 Seirzures
 Limited speech ability
 It is caused by a genetic deletion, which is the loss of a
DNA segment
The most common of the deletion syndromes
Traits Inherited Through DNA
 Personality traits or habits can be inherited through DNA
 There is a strong association of the A1 allele and the
DRD2 gene in the alcoholism trait
 This basically means that children of one or more
parents that are dependent upon alcohol are 50% more
likely to develop the problem
Forensic DNA Testing
 DNA tests are the more powerful piece of evidence that
a lawyer can have
 Samples are taken from the crime scene
Hair, Skin, Bodily fluids
 Samples are also taken from the suspect.
 They DNA samples are then taken from each, and if the
DNA matches, then the suspect is guilty as charged.
Sources
http://ghr.nlm.nih.gov/handbook/basics/dna
http://www.biologycorner.com/worksheets/DNAcoloring.html
http://www.thetech.org/genetics/ask.php?id=288
http://en.wikipedia.org/wiki/Punnett_square
http://web4health.info/en/answers/add-alcohol-inherited.htm
http://library.thinkquest.org/28599/courtroom.htm
http://en.wikipedia.org/wiki/DNA