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EVOLUTION OF POPULATIONS

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Bottleneck examples. One real life example of a species being affected by the bottleneck effect is the northern elephant seal. Humans intensely hunted these animals ... – PowerPoint PPT presentation

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Title: EVOLUTION OF POPULATIONS


1
EVOLUTION OF POPULATIONS
  • CHAPTER 16

2
POPULATION GENETICS
  • Study of evolution from a genetic point of view.
  • Study of the change in the GENE POOL for a
    population
  • Example- in a garden what percent of the roses
    are Red (RR), pink (Rr) or white (rr)

3
ALLELES
  • Possible traits of a gene
  • ALLELE FREQUENCY- how common a specific allele
    is in the gene pool
  • PHENOTYPE FREQUENCY- how common a specific
    phenotype is in a population

4
Allele frequency
5
ALLELE FREQUENCIES vsPHENOTYPE FREQUENCIES
  • Although phenotype frequencies tend to change
    generation to generation. Allele frequencies
    tend to stay the same.
  • HARDY WEINBERG EQUILIBRUIM---
  • p2 2pq q2 1

6
HARDY WEINBERG EQUILIBRUIM-
  • 1.    mutation is not occurring
  • 2.   there is no migration in or out of the
    population
  • 3.   the population is infinitely large
  • 4.   natural selection is not occurring
  • 5.   all members of the population breed
  • 6.   everyone produces the same number of
    offspring
  • 7.   all mating is totally random

7
Mutations
  • Can add a new allele into the mix
  • IMMIGRATION or EMIGRATION- can add or subtract
    a bunch of individuals with one specific allele

8
Small Populations
  • GENETIC DRIFT- the alelle frequency chances
    simply due to chance
  • link to Simulation notice how the value for P
    will either climb to 1 or go all the way down to
    0
  • http//darwin.eeb.uconn.edu/simulations/drift.html

9
No natural selection
  • All individuals have to have an equal chance of
    survival reproduction and have the same fitness.

10
Random Mating (No Sexual Selection)
  • NO ASSORTATIVE MATING
  • All individuals must reproduce at the same rate.

11
Bell Curve of Phenotypes
12
STABILIZING SELECTION
  • Individuals with the most average form of a trait
    have the highest fitness
  • Graph gets taller and narrower in the middle

13
Bell Curve of Phenotypes
14
DIRECTIONAL SELECTION
  • Individuals that have one extreme of a trait show
    a higher fitness
  • Center of the graph moves in one direction

15
Bell Curve of Phenotypes
16
DISRUPTIVE SELECTION
  • Individuals at either extreme have the highest
    fitness
  • This can lead to one species become two
    different species.
  • Single parabola slowly turns into 2 parabolas

17
Bell Curve of Phenotypes
18
Microevolution vs macroevolution
  • Micro-- small changes in a species
  • Macro- large transformations in a species

19
microevolution
  • is the changes in allele frequencies that occur
    over time within a population. This change is due
    to four different processes mutation, selection
    (natural and artificial), gene flow, and genetic
    drift.

20
Genetic drift ----or allelic drift
  • is the change in the frequency of a gene variant
    (allele) in a population due to random sampling.
  • occurs in smaller populations much faster

21
FOUNDERS EFFECT
  • is the loss of genetic variation that occurs when
    a new population is established by a very small
    number of individuals from a larger population.

22
BOTTLENECK-
  • a sharp reduction in size of a population due to
    environmental events (such as earthquakes,
    floods, fires, or droughts) or human activities.

23
Bottleneck examples
  • One real life example of a species being affected
    by the bottleneck effect is the northern elephant
    seal. Humans intensely hunted these animals in
    the late nineteenth century, and their population
    was reduced to just twenty at one point. Though
    the species has recovered and there are over
    30,000 northern elephant seals today, there is
    not a lot of genetic diversity among members of
    this species.

24
Why is a bottleneck bad?
  • Less genetic diversity
  • More likely to reveal RECESSIVE genes

25
Bottleneck examples
  • --Any ENDANGERED SPECIES
  • ---Giant Panda
  • --- Prairie Chicken
  • --- Amish
  • ---Inhabitants of small islands (Iceland)

26
Microevolution by ISOLATION
  • REPRODUCTIVE ISOLATION-- individuals are split
    from the rest of the population due to some type
    of barrier

27
Types of isolation
  • GEOGRAPHIC ISOLATION- populations that have been
    separated by physical barriers
  • --Mountain ranges
  • --Rivers- (Grand Canyon)
  • --Ocean- (organisms separated on different
    islands)
  • --Human Interference ---dams, highways, fences

28
Types of isolation
  • BEHAVIORAL ISOLATION (ethological)--- various
    courtship rituals or other behaviors interfere
    with interbreeding
  • Ex- Eastern and Western Meadowlark have different
    songs.
  • Crickets are very species specific in their songs

29
Types of isolation
  • TEMPORAL ISOLATION-- species that reproduce at
    different times
  • Flocks of Canadian Geese migrating at different
    times
  • Flowers that bloom at different times

30
TEMPORAL ISOLATION-
31
Prezygotic vs postzygotic barriers
  • PREZYGOTIC-- prevents reproduction- (geographic,
    temporal, behavioral)
  • POSTZYGOTIC BARRIER-
  • Hybrid inviability hybrid fails to develop or
    fails to reach sexual maturity- usually due to
    chromosomal differencesBehavioral sterility
    hybrid reaches sexual maturity but fails to
    produce appropriate courtship displays or mating
    behavior (plants may grow flowers that fail to
    attract pollinators)Hybrid sterility hybrids
    fail to produce functional gametes

32
macroevolution
  • Large changes in a species
  • Rate of EVOLUTION
  • 1. GRADUALISM
  • 2. PUNCTUATED EQUILIBRIUM

33
GRADUALISM
  • Defined as a profound change being the sum of
    many slow and steady changes
  • Ex- ostrich wings becoming smaller and smaller
    as the birds evolved.

34
Punctuated equilibrium
  • rapid evolution due to large changes in the
    environment
  • Examples-
  • volcanoes forming new islands
  • Small group becomes isolated
  • New species enters the ecosystem

35
ADAPTIVE RADIATION
  • Single species or small group of species evolves
    into several different forms
  • Ex- Mammals where quite small species during
    the days of the dinosaur. When the dinosaurs
    went extinct many species began large changes.
  • (elephants, whales, rhino)
  • Darwins finches- one species of finch turns
    into many different species.

36
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