The DNA Connection
DNA
• Deoxyribonucleic acid
• Genetic material that
carries information
about an organism and is
passed from parent to
offspring.
• 1953: Watson and Crick
figure out the structure
of DNA (double helix).
The Genetic Code
• Genes control the production of
proteins.
• Proteins determine:
–
–
–
–
Size
Shape
Color
Many other traits of an organism
Structure of DNA
• Looks like a twisted
ladder
• Two sides of the ladder:
– Made up of
alternating molecules
of deoxyribose and
phosphates
• Each rung is made up of
a pair of molecules
called nitrogen bases.
Genes and DNA
• DNA molecule – made up
of 4 nitrogen bases
• Adenine (A) and Thymine (T)
• Guanine (G) and Cytosine (C)
• (A) only pairs with (T)
• (G) only pairs with (C)
Mutations
• Any change in a gene or chromosome
• Mutation – Latin word that means “change”
What happens when a mutation occurs?
• Organism’s trait,
or phenotype,
may be different
from what it
normally would
have been.
Three Types of Mutations
• Substitution – One base pair is substituted
for another
• Deletion – One base pair is removed
• Addition – One base pair is added
Effects of Mutations
• A mutation is harmful if
it reduces the
organism’s chance for
survival and
reproduction.
Example: white lemurs
Effects of Mutations
• Helpful mutations
improve an
organism’s chances
for survival and
reproduction.
• Example: Antibiotic
resistance in bacteria.
Think about it!
• We can use DNA fingerprinting to
catch criminals. Should
Americans be forced to give DNA
samples so everyone is on file to
make it easier to catch criminals?