Genetics

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Genetics

• Ch. 14
• Multiple alleles for most traits
• Co-dominance is most common state
• How many alleles are carried by an individual?
• How many possible in a population?

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• Ch. 16, pages 266 - 271
• Ch. 17, pages 281 - 288

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Review

• How are traits passed on to the next generation?

Where does the variation in traits come from?
Why is variation important?
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Evolution

• How would you define it?

What evidence is there that evolution occurs?
What is the mechanism of this change?
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Natural Selection as a Mechanism

• Charles Darwin - 1844

• Alfred Russell Wallace - 1858

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• On the Origin of Species by Means of Natural
  Selection or the Preservation of Favoured Races
  in the Struggle for Life.

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Darwins Mechanism

• 1. Each species produces more offspring than
  survive.
  

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Darwins Mechanism

• 2. There is variation within the offspring.

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Darwins Mechanism

• 3. The offspring are in competition for limited
  resources.

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Darwins Mechanism

• 4. The best competitors survive to reproduce.
  They are the most fit.

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Darwins Fate
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Key Terms

• Gene Pool
• All the various alleles for all traits of a
  population.

• Population
• All the individuals in one area at one time of
  one species

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Key Terms

• Fitness
• the ability of an organism to survive and
  reproduce in its environment

• Adaptation
• an inherited trait that leads to fitness

How does an adaptation arise in a population?
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Steps in Evolution

• Mutation gives rise to genetic variation.

• Genetic variation results in differential
  adaptedness.

• Differential adaptedness results in differential
  reproduction.

• More individuals in population express the
  inherited characteristic.

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Evolutionthe change in allele frequency in a
population over time
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Lecture Activity

• What are the steps that led to the evolution of a
  flower that is mouse pollinated from one usually
  pollinated by a bird?
  
• Step One - a mutation(s) arise(s) in an
  individual resulting in variation.
  
• You complete the list of steps.

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• Does selection occur on the genotype or the
  phenotype?

What does that imply about the fate of recessive
alleles?
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Evolution

• Genetic variation arises by chance.

• Evolution is not directed from within organism.
  Those not fit for the present environment do not
  reproduce as much as those that are fit.

• Alleles for successful traits increase.

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Flower Evolution

• Plant would be better adapted if it changed
  pollinators, so gradually the plants acquire a
  yeasty-scented, brown flower close to the ground.
  Plants in each generation became more yeasty,
  brown and close to the ground than their parents
  did.

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Flower Evolution

• Because the environment of the plants ancestors
  favored more mice than birds, mutant individuals
  arose that had more mouse-attractive flowers.
  Selection favored these individuals, and
  eventually all of them had mouse-attractive
  flowers.

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Flower Evolution

• The existence of strategies as complex as
  mouse-attractive flowers cannot be explained by
  traditional evolutionary theory because
  structures like these are too complex to arise by
  chance.

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Flower Evolution

• Because the ancestors of these plants needed to
  change pollinators, nature allowed them to
  develop the ability to produce mouse-attractive
  flowers.

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Flower Evolution

• The plant evolved mouse-attractive flowers to
  protect attract a new pollinator.

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Hardy-Weinberg Law (No evolution)

• 1. No mutations.
• 2. Mating is random. No sex selection.
• 3. No gene flow (no migration).
• 4. No selection.
• 5. No genetic drift.
• large population unaffected by chance changes (a
  reduction) in allele frequency
  

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Genetic Drift

• Chance events that reduce allele frequency in a
  population

• Natural disasters (bottleneck effect)

• Beginning a new population (founder effect)

• Greater effect on small populations

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Speciation

• Biological Species Concept- all individuals that
  share many characteristics and are able to breed
  with each other sharing a gene pool.
  

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Speciation

• 1. Temporal
• 2. Geographic
• 3. Mechanical
• 4. Gametic incompatibility
• 5. Behavioral (Does not apply to plants.)
• 6. Strategy change

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Artificial Selection

• Brassica oleracea
• Cabbage
• Broccoli
• Cauliflower
• Brussels Sprouts
• Kohlrabi