Gregor Mendel (1822-1884)

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Gregor Mendel (1822-1884) the Foundations of
Genetics
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MutationPoint Mutations

• Change in one base pair - may or may not change
  amino acid, changed amino acid may or may not
  change protein conformation
• Spontaneous, but also increased by radiation,
  heat, chemical mutagens
• Rate Infrequent one in a billion bases

AATAAGAA
AATATGAA
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Three Point Mutations
Deletion
AATAAGAA
AATAGAA
Substitution
AATAAGAA
AATATGAA
Insertion
AATAAGAA
AATAAAGAA
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Three Genetic Mutations
Deletion
AATAAGAATGGG
AATAGAATGGG
Substitution
AATATGAATGGG
AATAAGAATGGG
Insertion
AATAAGAATGGG
AATAAAGAATGGG
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Chromosomal Mutations

• Chromosomes can be duplicated, portions can be
  translocated to a different chromosome or
  inverted on the same, or deleted
• Usually has profound consequences - sterility or
  worse
• Common, e.g. Downs syndrome 1700 births
• Major mode of instantaneous speciation in
  self-fertilizing or inbreeding species,
  especially plants

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Human genomes are complex, but .

• Only 1/3 more genes than a worm
• - Genes like components in assembly lines?
• Many more harmful mutations per generation
• Much less coding DNA (rest junk or spacer or ?? )

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Genetic Load

• For humans, estimated by reduced fertility and
  increase in birth defects associated with
  conceptions between relatives
• 4 recessive lethals per individual, more than one
  new lethal per generation
• In womens eggs, chromosomal defects in eggs
  increase with age
• In mens sperm, DNA sequence changes increase
  with age
• In outbred human conceptions
• 70 of conceptions never come to term
• 2 per 1000 live births have genetic defects

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What Changes Gene Frequencies?

• Mutation
• Genetic drift (random change in small pops)
• Non-random Mating
• Migration Gene Flow
• Natural Selection

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Purifying Selection

• Dominant or Sex-linked (X or Y) deleterious
  mutant alleles eliminated rapidly by natural
  selection
• Recessive autosomal deleterious mutant alleles
  reduced slowly by selection
• heterozygotes protect recessive deleterious
  mutant alleles
• never eliminated a mutation - selection
  equilibrium is reached

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Stabilizing Selection decreases variation,
doesnt shift mean
Mean
Old Mean
Frequency
Frequency
Trait value
Trait value
Parents
Offspring
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Directional Selection may reduce variation,
shifts mean
Mean
Old Mean
Frequency
Trait value
Parents
Offspring
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Disruptive Selectionincreases variation, may
shift mean
Mean
Old Mean
Frequency
Trait value
Parents
Offspring
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Sexual Selection
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Forms of Sexual Selection

• Intrasexual (usually male-male competition)
• Weapons for within-sex competition
• Intersexual (usually females choosing males)
• Ornaments or signals to attract choosy mates
• Why are animals choosy aesthetic preferences
  (Darwins hyp.) or signals indicate mate quality?

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Consequences of Sexual Selection

• Drives species away from the ecological optimum
• Major cause of sexual dimorphism via disruptive
  selection since ornaments are an advantage in
  only one sex, there is selection for modifiers
  that lead to expression in one sex only