Chapter 17.2 Genetic Change 17.3 Speciation

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Chapter 17.2 Genetic Change 17.3 Speciation
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Definitions

• Gene pool All alleles of the populations genes.
• Allelic frequency of a specific allele in the
  gene pool. Example See Figure 5 Page 404
  Snapdragon Flower
• Genetic Equilibrium This exists when the
  frequency of alleles remains the same over
  generations. The population is not evolving.

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5 Different Forces That Can Cause Evolution

• 1. Gene Flow
• 2. Non-random Mating (Sexual Selection)
• 3. Mutation
• 4. Genetic Drift
• 5. Natural Selection

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Gene Flow

• Gene Flow occurs when genes are added or removed
  from a population
• Example Migration
• These caribou are migrating from one place to
  another. If they meet other groups of caribou
  and interbreed, gene flow may occur.

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Non-random Mating (Sexual Selection)

• Females sometimes select mates based on the
  males size, color, ability to gather food, or
  other characteristics.
• Example The vibrant red stripe of the blue
  muzzle of this male (right) mandrill baboon does
  not appear in females (left).

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Non-random Mating (Sexual Selection)
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Mutation

• When the DNA code of organisms changes randomly
  (Creates new alleles)

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Genetic Drift

• Chance events, such as fires, floods or storms,
  can cause rare alleles to be lost.
• This occurs more often in populations that are
  small in size. Genotypes
• can change as a result.
• Example A wildflower population ... consisted
• of only 25 plants. Assume that 16 of the plants
• have the genotype AA for flower color, 8 are Aa,
  and only 1 is aa. Now imagine that three of the
  plants are accidently destroyed by a rock slide
  before they have a chance to reproduce. By
  chance, all three plants lost from the population
  could be AA individuals.

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Natural Selection

• Can remove individuals with certain traits from a
  population.
• The alleles for those traits may become less
  common in the population over time.
• Example Horse Evolution

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Evolutionary Fitness

• How long an individual can survive and how many
  offspring they can produce to pass genes to
  future generations???
• This is their Evolutionary Fitness.

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Who has the Higher Evolutionary Fitness?
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3 Types of Natural Selection

• Directional Selection favors one of the extreme
  variations of a trait
• Stabilizing Selection favors average
  individuals
• Disruptive Selection favors individuals with
  both extremes of a trait (eliminates intermediate
  phenotypes)

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17.3 Biological Species Concept

• When Males and Females of the same species
  reproduce and their offspring are fertile and can
  pass on their genes they are considered a species.

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Sterile Hybrids
Mule
Liger
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Speciation

• Speciation occurs when members of similar
  populations no longer interbreed to produce
  fertile offspring within their natural
  environment.
• Example Squirrels that live in the Grand Canyon

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Species definition does not always apply

• Some organisms reproduce Asexually
• Bacteria and Archaebacteria

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Types of Speciation

• a. Geographic Barrier- A physical barrier that
  prevents interbreeding (Mountain, River, Island)
• b. Change in Mating Behavior and Timing
• c. Change in Niche (Food source)

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a. Geographic Isolation
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Geographic Isolation

• Examples of how this can happen
• A pond dries up somewhat to make two ponds,
• A river becomes re-routed so that it cuts through
  a field,
• Two land masses drift apart over time,
• A few seeds stuck on a bird's feather fall by
  chance on a new island
• A new road goes up between 2 fields,
• A flood washes a small population of lizards to
  an island....etc

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Geographic Isolation
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Change in b. Mating Behavior and Timing

• Many species that sexually reproduce have
  specific behaviors for attracting mates, such as
  a pattern of sounds or actions.
• Example The pickerel frog and the leopard frog
  are closely related species. Differences in
  mating times may have caused their reproductive
  isolation.

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Timing

• Similar species have different breeding
  seasons
• Eastern Spotted Western Spotted
• Skunk Skunk

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Bizarre Mating Rituals

• The male anglerfish latches onto the female like
  a parasite, living off her food and fertilizing
  her when she's ready to lay eggs.
• The male octopus's penis breaks off during
  mating, but don't worry, it will grow back the
  following season.

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Bizarre Mating Rituals

• Emperor Penguins travel as far as 70 miles on
  foot to reach the breeding site. They look for
  their mates by making a bugling call. Once they
  find one another, they stand breast to breast,
  repeatedly bow to each other and sing.

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c. Change in Niche

• Divergence can happen when populations use
  different niches
• Example The members of a particular population
  of insects live and feed high up in the trunks of
  trees. As time passes, some members of the
  population begin to feed on different parts of
  the trees. Eventually the 2 groups diverge and no
  longer interbreed.

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Artificial Speciation
Diane Dodds fruit fly lab, 1989
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What is Extinction?

• When a species fails to produce any offspring
• 99 of all species that have ever lived on Earth
  are now extinct

Wooly Mammoth
T Rex
Dodo Bird
Tasmanian Tiger
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The End