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Evolution: The Role of DNA
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DNA – The Molecule of Life
• DNA is the
genetic
blueprint of life.
• Within every
living cell,
chromosomes
can be found
that contain the
DNA and genes
that govern the
cell.
Structure of DNA
• DNA consists of 2
strands. Each strand
is made up of a series
of sugar and
phosphate molecules
which are chemically
bonded to
nitrogenous bases.
These bases then
bond to each other to
hold the strands
together.
• When the 2 strands
are joined together
they form a spiraling
ladder, also known as
a double helix.
Nitrogenous Bases
There are four types of nitrogenous
bases which make up the center
rungs of the DNA ladder;
1.
2.
3.
4.
Adenine
Thymine
Guanine
Cytosine
Above: Adenine and Thymine
Below: Guanine and Cytosine
The order that these bases are found
in determines the gene
sequences on the DNA
molecule.
Note: Adenine will only pair up with
Thymine and Guanine will only
pair up with Cytosine (termed
complementary base pairing)
Note that adenine and guanine are double
ringed structures whereas thymine and
cytosine only contain single rings
DNA and Variability
• If genes are determined by the DNA molecule, and if
traits are determines by genes, then DNA determines
your traits
• Mutations can occur in the DNA molecule which
allows for variation in a species (whether those
mutations be for the better or the worse)
• If the new traits are preferred for the environment that
it lives in that individual will go on to reproduce and
produce offspring.
• The possible passing on of these traits to offspring by
sexual reproduction allows for that variation to
continue and increase in frequency in that population
• Variation in genes is the key to evolution
What we mean when we say the word
“evolution”
Evolution is simply put, gradual change in
the genetic composition of a population
during successive generations.
To say that you believe in general evolution
simply means that you agree with the fact
that genes will change over time due to
sexual reproduction. This is an irrefutable
fact.
Microevolution
• Refers to the minor changes that accompany shortterm adaptations to changing environments (this
could be in an animal, plant or any living cell)
• It is the result of genetic variation within a species or
population acted on over time by a process called
natural selection (more to come….)
• Changes involved might include differences in color,
size or behavior that are better suited towards a new
environment
• These minor changes may or may not be enough to
actually create a new species
Macroevolution
• Refers to evolution “above the species level”
• In effect, macroevolution looks back along the lines of
common descent, using comparative anatomy,
embryology, biochemistry and paleontology to
reconstruct pathways of descent from one species to
another species
• It requires the extensive use of inference in the
development of explanations, which can create
uncertainty for some individuals