Module 6 Lecture 3 Processes in Evolution

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Module 6 Lecture 3 Processes in Evolution

• Evolution requires
• 1. Sources of novelty
• 2. A process which promotes advantageous
  novelties
• An early theory Lamarkism
• the inheritance of acquired characteristics
• Note that Lamark (1744-1829) knew no genetics.
  Nor did Darwin (1809-1882)

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Lamarkism- The evolution of the giraffes neck

• The short-necked ancestor stretches to browse
  leaves and lengthens its neck
• This characteristic is acquired by its offspring
  and over many generations the long neck is
  evolved.
• Weissman barrier makes the inheritance of
  acquired traits unlikely

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The Modern Synthesis ( Neodarwinism)

• Early 19th century amalgam of Darwinism,
  Mendelism and mathematics.
• This is the foundation of evolutionary theory
  today
• Molecular biology has added a fourth pillar of
  support to this.

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Basic concepts

• Population and Gene pool
• Evolution requires more than one individual!

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Microevolution and Macroevolution

• Micro- is described in terms of changes in gene
  frequencies
• Macro- is seen in the fossil record
• Micro ? Macro.
• i.e. Changes in gene frequencies may give new
  species which (given enough time) may lead to new
  genera, families etc. Example of the evolution
  of the horse, next slide.

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Hardy-Weinberg Theorem

• H-W says (in summary) that
• Gene and genotype frequencies do not change from
  one generation to the next, unless acted upon by
  the agents of evolution.
• (Note for gene read allele).

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Fig. 23.3a
make different
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Fig.23.3
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Hardy-Weinberg Theorem as a Starting Point

• H-W describes the genetic steady-state
• Microevolutionary processes upset this
  equilibrium
• H-W gives us a mathematical foundation from which
  rates of change in gene frequencies can be
  calculated.

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Agents of Evolution 5 Causes of microevolution

• 1. Genetic drift
• 2. Gene flow
• 3. Mutation
• 4. Non-random mating
• 5. Natural selection.

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1. Genetic Drift

• In small populations chance (sampling errors)
  will cause gene frequencies to change.

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2.Gene flow3. Mutation

• Gene flow means movement of genes between
  populations due to migration
• Mutation is the ultimate source of genetic
  novelty but is a rare event and more often
  produces neutral or deleterious mutants as
  beneficial ones.

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4. Non-random matingFig.23.6 Assorative
matingin toads

• Assortative mating involves like with like or
  alternatively attraction of opposites not at
  random.

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• 1 to 4 above are the sources of phenotypic
  novelty
• Number 5. Natural selection promotes advantageous
  novelties.