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Module 6 Lecture 3 Processes in Evolution

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Title: Module 6 Lecture 3 Processes in Evolution


1
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)

2
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

3
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.

4
Basic concepts
  • Population and Gene pool
  • Evolution requires more than one individual!

5
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.

6
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7
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).

8
Fig. 23.3a
make different
9
Fig.23.3
10
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.

11
Agents of Evolution 5 Causes of microevolution
  • 1. Genetic drift
  • 2. Gene flow
  • 3. Mutation
  • 4. Non-random mating
  • 5. Natural selection.

12
1. Genetic Drift
  • In small populations chance (sampling errors)
    will cause gene frequencies to change.

13
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.

14
4. Non-random matingFig.23.6 Assorative
matingin toads
  • Assortative mating involves like with like or
    alternatively attraction of opposites not at
    random.

15
  • 1 to 4 above are the sources of phenotypic
    novelty
  • Number 5. Natural selection promotes advantageous
    novelties.
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