Evolution PowerPoint II

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Evolution PowerPoint II

• Sources of variation and the results of genetic
  variation.

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Lesson Goals.

• Students will be able to
• Describe where the genetic variation in a species
  comes from.
• Understand the results of genetic variation.
• Explain how changing environmental conditions
  affect the rate of evolution.
• Predict what will happen to a species that cannot
  adapt to a changing environment.

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Sources of variation

• There are two possible sources of variation
  within a population.
• 1. Mutation A mutation is the change in the
  base sequence of DNA.
• Mutations that occur in the gametes (sex cells)
  can be passed on to the offspring in sexual
  reproducing organisms.
• Nearly all mutations are harmful.

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Beneficial mutations

• While the majority of mutations are not
  beneficial, sometimes random changes in the DNA
  give an individual a competitive advantage.
• An example of a beneficial mutation occurred in
  peppered moths.
• Lets take a look at what happened with these now
  famous moths.

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Peppered moths

• Before the industrial revolution, the dominant
  color of the peppered moth was a very light
  color.
• This allowed them to blend in with the tree
  trunks, which were also light colored.
• Pollution caused the trees to be covered with
  soot, darkening them and making the white moth
  stand out and become much more vulnerable to
  predation.
• A mutation for dark colored moths which once had
  a low adaptive value now had a much higher one.

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Genetic shuffling

• In sexually reproducing species, the far greater
  source of variation is comes from the shuffling
  of genes during meiosis and fertilization.
• Asexual reproducing species lack this source of
  variation in virtually all cases.
• Some unicellular organisms DO exchange genetic
  material with each other, but they do not need to
  in order to reproduce.
• This process is called conjugation.

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Evidence for evolution.

• There are several different sources of evidence
  for evolution.
• 1. Fossil Records
• 2. Homologous Structures
• 3. DNA similarities
• 4. Genetic changes within species

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Fossils

• Remains of animals and plants found in
  sedimentary rock deposits give us an
  indisputable record of past changes through
  time.  This evidence attests to the fact that
  there has been a tremendous variety of living
  things.  Some extinct species had traits that
  were transitional between major groups of
  organisms.  Their existence confirms that species
  are not fixed but can evolve into other species
  over time.

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Homologous structures

• Many groups of species share the same types of
  body structures because they inherited them from
  a common ancestor that had them.  This is the
  case with the vertebrates , which are the
  animals that have internal skeletons.  The arms
  of humans, the forelegs of dogs and cats, the
  wings of birds, and the flippers of whales and
  seals all have the same types of bones (humerus,
  radius, and ulna) because they have retained
  these traits of their shared common ancient
  vertebrate ancestor.

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DNA

• All of the tens of thousands of types of proteins
  in living things are made of only 20 kinds of
  amino acids.  Despite the great diversity of life
  on our planet, the simple language of the DNA
  code is the same for all living things.  This is
  evidence of the fundamental molecular unity of
  life.
• The DNA code is most similar between closely
  related species. Humans and Chimpanzees share
  over 98 of their genes.

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Genetic change within a species

• This process of natural selection resulting in
  evolution can be easily demonstrated over a 24
  hour period in a laboratory Petri dish of
  bacteria living in a nutrient medium.  When a
  lethal dose of antibiotic is added, there will be
  a mass die-off.  However, a few of the bacteria
  usually are immune and survive.  The next
  generation is mostly immune because they have
  inherited immunity from the survivors.   

•  

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Video

• Isn't evolution just a theory?