Microevolution (Ch 23) and Macroevolution (Ch 24)

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Microevolution (Ch 23) andMacroevolution (Ch 24)
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Gene Pools
A gene pool is the sum of alleles within a
population
A population is a localized group of organisms of
the same species
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Microevolution
Macroevolution

• Changes occurring in a population
• Adaptations result in evolution
• Evolution above the species level
• Origin of new taxonomic groups

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Hardy-Weinberg Equilibrium

• To assume Hardy-Weinberg equilibrium all of the
  following must be true
• The population must be very large (no sampling
  error/genetic drift)
• There must be no mutation
• There must be no natural selection
• No migration between populations
• Random mating

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Hardy-Weinberg Equation

• pfrequency of one allele (A)
  qfrequency of
• 
  the other allele(a)
• pq1.0 p1-q q1-p
• p2 frequency of AA genotype 2pqfrequency
  of Aa genotype q2 frequency of aa genotype
• frequencies of all individuals must add to 1
  (100)
• p2 2pq q2 1

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Hardy Weinberg Equilibrium
Population of cats n100 16 white and 84
black bb white B_ black
Can we figure out the allelic frequencies of
individuals BB and Bb?
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Using Hardy-Weinberg equation
q2 (bb) 16/100 .16 q (b) v.16 0.4 p (B) 1
- 0.4 0.6
population 100 cats 84 black, 16 white How many
of each genotype?
p2.36
2pq.48
q2.16
bb
Bb
BB
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Hardy Weinberg Ex 1

• If only 6 of the population displays pale eyes
  (recessive gene e), what is the frequency of
  genotype Ee in this population?
• q2 0.06 ---gt q 0.24
• p q 1 ---gt p 0.76
• Ee 2pq 2(0.76)(0.24) 0.36

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Hardy Weinberg Ex 2

• If the statistics for people who have PKU is 1 in
  10,000, what percentage of the US population
  carries the gene but does not exhibit the
  disease?
• q2 0.0001 ---gt q 0.01
• p q 1 ---gt p 0.99
• 2pq 2(0.99)(0.01) 0.0198 or 1.98

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Genetic Drift
Genetic drift is random fluctuation in allele
frequency between generations.
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A Genetic Bottleneck is a Form of Genetic Drift
In a genetic bottleneck, allele frequency is
altered due to a population crash.
Once again, small bottlenecked populations big
effect.
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Genetic Bottleneck A Historical Case
A severe genetic bottleneck occurred in northern
elephant seals.
Other animals known to be affected by genetic
bottlenecks include the cheetah and both ancient
and modern human populations.
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Founder Effect- new habitat
The South Atlantic island of Tristan da Cunha was
colonized by 15 Britons in 1814, one of them
carrying an allele for retinitis pigmentosum.
Among their 240 descendents living on the island
today, 4 are blind by the disease and 9 others
are carriers.
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Gene Flow

• genetic exchange due to the migration of fertile
  individuals or gametes between populations
  (reduces differences between populations)
• seed pollen distribution by wind insect
• migration of animals

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Migration (Gene Flow)
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Mutations

• Mutation creates variation
• a change in an organisms DNA (gametes many
  generations) original source of genetic
  variation (raw material for natural selection)

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Nonrandom Mating

• Inbreeding
• assortive mating- choosing a mate with either
  similarities or differences (both shift
  frequencies of different genotypes)

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Sexual selection
Its FEMALE CHOICE, baby!
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Natural Selection

• differential success in reproduction
• climate change
• food source availability
• predators, parasites, diseases
• toxins
• only form of microevolution that adapts a
  population to its environment
• provides fitness increase in the population

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Genetic Variation

• Polymorphism- 2 or more distinct forms (morphs)
  within a single population of organisms

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Geographic Variation-cline

• differences in genetic structure between
  populations

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Mutation and Sexual Recombination

• -random changes to DNA
• errors in mitosis meiosis
• environmental damage

-Recombination mixing of alleles
new combinations new phenotypes
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Diploidy

• 2nd set of chromosomes
• hides variations in the
• heterozygote
• Balanced polymorphism
  heterozygote advantage (hybrid vigor i.e.,
  malaria/sickle-cell anemia)

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In reality there is little random mating

• Inbreeding can occur within small or isolated
  populations
• Mate selection- choosing a mate similar to ones
  self.(Homogamy)

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Sickle-Cell Prevalence
Selection by malaria exposure
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Evolutionary Fitness

• Contribution an individual makes to the gene pool
  for the next generation.
• The alleles of this individual promotes the
  survival or reproductive success of others that
  share the same allele.

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Modes of Selection

• Stabilizing Selection- favors the middle and
  eliminates the extremes in a population
• Directional Selection- natural selection or
  evolutionary changes in the population
• Disruptive Selection- favors the two extremes
  creating polymorphism.

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Modes of Selection
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Sexual Dimorphism

• Two distinct forms in the sexes of some species

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Sexual Selection
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Macroevolution the origin of new taxonomic
groups Chapter 24

• Speciation the origin of new species
• 1- Anagenesis (linear evolution) accumulation
  of heritable changes
• 2- Cladogenesis (branching evolution) budding
  of new species from a parent species that
  continues to exist (basis of biological diversity)

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What is a species?

• Biological species concept a population whose
  members have the potential to interbreed and
  produce viable, fertile offspring

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Other Species Concepts

• Biological Species Concept
• Reproductive Isolation
• Not necessarily easy to apply
• Morphological Species Concept
• Phenotypic differences
• Paleontological Species Concept
• Fossil species
• Ecological Species Concept
• Filling of ecological niches
• Phylogenetic Species Concept
• Evolutionary lineages/genetic history

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Reproductive Isolation (isolation of gene pools)

• Pre-zygotic barriers impede mating between
  species or hinder the fertilization of the ova
• Habitat (snakes water/terrestrial)
• Behavioral (fireflies mate signaling)
• Temporal (salmon seasonal mating)
• Mechanical (flowers pollination anatomy)
• Gametic (frogs egg coat receptors)

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Reproductive Isolation

• Post-zygotic barriers fertilization occurs, but
  the hybrid zygote does not develop into a viable,
  fertile adult
• Reduced hybrid viability (frogs zygotes fail to
  develop or reach sexual maturity)
• Reduced hybrid fertility (mule horse x donkey
  cannot backbreed)
• Hybrid breakdown (cotton 2nd generation hybrids
  are sterile)

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Modes of speciation (based on how gene flow is
interrupted)

• Allopatric populations segregated by a
  geographical barrier adaptive radiation
  diversification due to habitat change (Darwins
  finches)
• Sympatric reproductively isolated subpopulation
  in the midst of its parent population

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Sympatric Speciation

• Polyploidy-more than 2 paired chromosomes
• Allopolyploidy- infertile hybrid
• Sexual selection- intraspecies competition

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Tempo of speciation

• Gradualism- species diverge more and more as they
  adapt
• Punctuated Equilibrium- periods of apparent
  stability and then a sudden change

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Evolutionary Novelties

• Exaptation- structures becomes better adapted
  for another function- bird feathers originally
  kept the bird warm but later were better suited
  for flight
• Heterochromy- change in the rate of evolution-
  foot development in salamanders
• Paedomorphosis- retaining some juvenile
  characteristics

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Convergent Evolution
Analogies are products of convergent evolution
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