Evolution - The Role of DNA

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Evolution The Role of DNA
www.onacd.ca
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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.

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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.

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Nitrogenous Bases

• There are four types of nitrogenous bases which
  make up the center rungs of the DNA ladder
• Adenine
• Thymine
• Guanine
• 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)

Above Adenine and Thymine Below Guanine and
Cytosine
Note that adenine and guanine are double ringed
structures whereas thymine and cytosine only
contain single rings
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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

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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.

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Microevolution

• Refers to the minor changes that accompany
  short-term 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

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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