Population genetics and evolution

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Population genetics and evolution

• What is evolution?

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Population genetics and evolution

• What is evolution?
• Descent with modification

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Population genetics and evolution

• What is evolution?
• Descent with modification
• A change in the characteristics of a population
  over time

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Population genetics and evolution

• What is evolution?
• Descent with modification
• A change in the characteristics of a population
  over time
• A change in the genetic composition of a
  population over time (the frequency of genes)

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Population genetics and evolution

• Some genetics terminology
• Chromosomes

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Population genetics and evolution
human karyotype fig here
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Population genetics and evolution

• Some genetics terminology
• Chromosomes
• Homologous chromosomes

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Population genetics and evolution
human karyotype fig here
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Population genetics and evolution

• Some genetics terminology
• Chromosomes
• Homologous chromosomes
• Locus

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Population genetics and evolution

• Some genetics terminology
• Chromosomes
• Homologous chromosomes
• Locus
• Alleles

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Population genetics and evolution

• Alleles
• Hemoglobin has two A chains and two B chains
• The B chains have several forms
• fetal
• adult normal
• adult sickle
• These are a result of alleles - different forms
  of the same gene at the same locus

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Population genetics and evolution

• Some genetics terminology
• Alleles may be dominant and recessive

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Population genetics and evolution

• Some genetics terminology
• Alleles may be dominant and recessive
• In Biston betularia, the gene for melanism is
  dominant (M)

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Population genetics and evolution

• Some genetics terminology
• Alleles may be dominant and recessive
• In Biston betularia, the gene for melanism is
  dominant (M)
• The gene for typical color is recessive (m)

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Population genetics and evolution

• Some genetics terminology
• Alleles may be dominant and recessive
• In Biston betularia, the gene for melanism is
  dominant (M)
• The gene for typical color is recessive (m)
• Each individual moth has two alleles
• MM and Mm are melanic, mm are typical

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Population genetics and evolution

• Gene frequencies
• The frequency of all of the alleles at a
  particular locus in a population 100 or 1.0

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Population genetics and evolution

• Gene frequencies
• The frequency of all of the alleles at a
  particular locus in a population 100 or 1.0
• If there are two alleles, the frequency of one
  p and the frequency of the other q

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Population genetics and evolution

• Gene frequencies
• The frequency of all of the alleles at a
  particular locus in a population 100 or 1.0
• If there are two alleles, the frequency of one
  p and the frequency of the other q
• p q 1.0

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Population genetics and evolution

• Gene frequencies
• The frequency of all of the alleles at a
  particular locus in a population 100 or 1.0
• If there are two alleles, the frequency of one
  p and the frequency of the other q
• p q 1.0
• Each individual has two alleles, one from each
  parent
• With sexual reproduction, p q alleles in the
  eggs are combined with p q alleles in the sperm

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Population genetics and evolution

• Gene frequencies
• (p q) x (p q) (p q)2 p2 2pq q2

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Population genetics and evolution

• Gene frequencies
• (p q) x (p q) (p q)2 p2 2pq q2
• In Biston betularia
• MM occurs with a frequency of p2
• Mm occurs with a frequency of 2pq
• mm occurs with a frequency of q2

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Population genetics and evolution

• Gene frequencies
• (p q) x (p q) (p q)2 p2 2pq q2
• In Biston betularia
• The population is composed of p2 homozygous
  melanic individuals, 2pq heterozygous individuals
  (which are melanic), and q2 homozygous typical
  individuals

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Population genetics and evolution

• Gene frequencies
• (p q) x (p q) (p q)2 p2 2pq q2
• In Biston betularia
• Phenotype frequencies
• Lets say for arguments sake that the population
  consists of 81 typical individuals and 19
  melanic individuals

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Population genetics and evolution

• Gene frequencies
• p2 MM, 2pq 2Mm, and q2 mm
• q2 .81
• what is q, the frequency of m?

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Population genetics and evolution

• Gene frequencies
• p2 MM, 2pq 2Mm, and q2 mm
• q2 .81
• what is q, the frequency of m?
• q 0.9 (0.92 0.81)

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Population genetics and evolution

• Gene frequencies
• p2 MM, 2pq 2Mm, and q2 mm
• q2 .81
• what is q, the frequency of m?
• q 0.9 (0.92 0.81)
• What is p, the frequency of M?

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Population genetics and evolution

• Gene frequencies
• p2 MM, 2pq 2Mm, and q2 mm
• q2 .81
• what is q, the frequency of m?
• q 0.9 (0.92 0.81)
• What is p, the frequency of M?
• p 0.1

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Population genetics and evolution

• Gene frequencies
• p2 MM, 2pq 2Mm, and q2 mm
• q2 .81
• what is q, the frequency of m?
• q 0.9 (0.92 0.81)
• What is p, the frequency of M?
• p 0.1
• p2 0.01 (MM), 2pq 0.18 (Mm)

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Population genetics and evolution

• Gene frequencies
• p2 MM, 2pq 2Mm, and q2 mm
• q2 .81
• what is q, the frequency of m?
• q 0.9 (0.92 0.81)
• What is p, the frequency of M?
• p 0.1
• p2 0.01 (MM), 2pq 0.18 (Mm)
• 19 of individuals are melanic

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Population genetics and evolution

• To summarize
• Homozygous dominants MM p2
• Heterozygotes Mm 2pq
• Homozygous recessives mm q2

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Population genetics and evolution

• What happens during reproduction?
• Meiosis separates alleles into gametes

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Population genetics and evolution

• What happens during reproduction?
• Meiosis separates alleles into gametes
• Gametes bear alleles in proportion to their
  frequency in the population

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Population genetics and evolution

• What happens during reproduction?
• Meiosis separates alleles into gametes
• Gametes bear alleles in proportion to their
  frequency in the population
• there are p sperm with M and q sperm with m

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Population genetics and evolution

• What happens during reproduction?
• Meiosis separates alleles into gametes
• Gametes bear alleles in proportion to their
  frequency in the population
• there are p sperm with M and q sperm with m
• there are p eggs with M and q eggs with m

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Population genetics and evolution

• What happens during reproduction?
• Meiosis separates alleles into gametes
• Gametes bear alleles in proportion to their
  frequency in the population
• there are p sperm with M and q sperm with m
• there are p eggs with M and q eggs with m
• Eggs and sperm combine to form zygotes

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Population genetics and evolution

• What happens during reproduction?

EGGS
SPERM M (p 0.1) m (q 0.9)
M (p 0.1) MM (p2 0.01) Mm (pq 0.09)
m (q 0.9) Mm (pq 0.09) mm (q2 0.81)
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Population genetics and evolution

• After reproduction
• Homozygous dominants MM p2 0.01
• Heterozygotes Mm 2pq 0.18
• Homozygous recessives mm q2 0.81
• Melanics 0.19 (0.01 0.18)
• Typicals 0.81

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Population genetics and evolution

• After reproduction
• Homozygous dominants MM p2 0.01
• Heterozygotes Mm 2pq 0.18
• Homozygous recessives mm q2 0.81
• Melanics 0.19 (0.01 0.18)
• Typicals 0.81
• THIS IS WHAT WE STARTED WITH!!

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Population genetics and evolution

• What is evolution? A change in gene frequency
  within a population

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Population genetics and evolution

• What is evolution? A change in gene frequency
  within a population
• What processes lead to changes in gene frequency?

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Population genetics and evolution

• processes that lead to changes in gene frequency

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Population genetics and evolution

• processes that lead to changes in gene frequency
• Mutation (the ultimate source of all genetic
  variation)

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Population genetics and evolution

• processes that lead to changes in gene frequency
• Mutation
• Gene flow (usually accomplished by migration of
  individuals from one population to another)

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Population genetics and evolution
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Population genetics and evolution

• processes that lead to changes in gene frequency
• Mutation
• Gene flow
• Non-random mating

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Population genetics and evolution

• processes that lead to changes in gene frequency
• Mutation
• Gene flow
• Non-random mating
• Selection (the most powerful agent of
  evolutionary change)

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Population genetics and evolution

• processes that lead to changes in gene frequency
• Mutation
• Gene flow
• Non-random mating
• Selection
• Genetic drift (changes in gene frequency in small
  populations due to random sampling error)

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Population genetics and evolution

• Genetic drift
• Changes in gene frequency in small populations
  due to random sampling error

Brown (br) 30 Yellow (y) 20 Red (r)
20 Orange (o) 10 Green (g) 10 Blue (bl)
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Population genetics and evolution

• Genetic drift
• Population bottlenecks - reduction of population
  size results in loss of genetic variation and
  potentially in the loss of alleles from the
  population
• Reduction of population size must be catastrophic
  and non-selective

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Population genetics and evolution

• Genetic drift Population bottlenecks

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Population genetics and evolution

• Genetic drift Population bottlenecks

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Population genetics and evolution

• Genetic drift Population bottlenecks

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Population genetics and evolution

• Genetic drift Population bottlenecks

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Population genetics and evolution

• Genetic drift
• The Founder Effect - a small population disperses
  from a larger population, and founds a new
  population in another geographic location. The
  gene frequencies in the founding population are
  not representative of the larger population.
• Especially important in speciation on
  archipelagoes

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Population genetics and evolution
Elepaio
Amakihi