Points to remember about Natural Selection - PowerPoint PPT Presentation

1 / 40
About This Presentation
Title:

Points to remember about Natural Selection

Description:

Natural selection only works on heritable variations, not acquired traits. ... members.tripod.com/~Alphacentaur/ X-men.JPG. Mutation ... – PowerPoint PPT presentation

Number of Views:49
Avg rating:3.0/5.0
Slides: 41
Provided by: floyd8
Category:

less

Transcript and Presenter's Notes

Title: Points to remember about Natural Selection


1
Points to remember about Natural Selection
  • Populations evolve, but individuals do not.
    I.E., Natural selection acts on the level of the
    individual, but populations are the smallest unit
    that can evolve.
  • Natural selection only works on heritable
    variations, not acquired traits.
  • Natural selection can only work with what its
    given. Variations are produced by different
    genetic mechanisms.
  • Natural selection is situational to a given
    environment in a given time and place.
  • No ideal organism.
  • Fitness of a given trait changes.

2
Population Genetics Microevolution
3
The historical context of Darwins life and ideas
4
Evolution is.
  • For Darwin (1859) Evolution is gradual change of
    heritable traits in a population across
    generations, eventually generating species over
    time.
  • For the Modern Evolutionary Synthesis (early 20th
    c.) Evolution is a change in allele frequency
    over time

5
Population Genetics - Terms
  • Population Localized group of individuals of the
    same species
  • Species Group of populations whose individuals
    can potentially interbreed
  • Gene Pool Total aggregate of genes in a
    population at one time
  • Allele an alternative form of a gene
  • Homozygous have identical alleles for a given
    trait (dominant or recessive) (e.g. AA or aa in a
    diploid)
  • Heterozygous have gt1 different alleles for a
    given trait (e.g. Aa or aA in a diploid)
  • Why arent all individuals of one species
    identical?

6
Genetic Diversity
1
1
7
Genetic Diversity is the product of
  • Sexual reproduction
  • Genetic recombination
  • Mutation- key form of genetic variation in
    asexual reproduction, substrate for new genetic
    material
  • Provides alternative alleles that may or may not
    be useful with changes in environment raw
    material for evolution
  • R.A. Fisher's Fundamental Theorem of Natural
    Selection the rate of natural selection is
    proportional to the degree of variation within a
    population

8
The Modern Evolutionary Synthesis in action
  • Hardy-Weinburg Equilibrium
  • p2 2pq q2 1

9
Figure 23.3a The Hardy-Weinberg theorem
10
Figure 23.3b The Hardy-Weinberg theorem
11
The Modern Evolutionary Synthesis in action
  • Hardy-Weinburg Equilibrium
  • p2 2pq q2 1
  • Assumptions
  • 1. Large population size
  • 2. No gene flow
  • 3. No mutation
  • 4. Random mating
  • 5. No selection

12
The Modern Evolutionary Synthesis in action
  • Microevolution (shift in allele frequencies)
    happens when the H-W assumptions fail !
  • Small population size gt Genetic Drift
  • Migration gt Gene Flow
  • Mutation
  • Natural Selection
  • Nonrandom mating

13
Genetic Drift random changes in allele (and
genotype) frequencies from generation to
generation due to sampling error
14
Genetic Drift, part A The bottleneck effect
Alleles in original population
Alleles remaining after bottleneck
15
Cheetah
Bottleneck effect
www.petsdoc.com/pics/funpages/ wildlifephotos/chee
tah.jpg
16
Northern Elephant Seal
Bottleneck Effect
  • http//www.icsi.berkeley.edu/dbailey/gallery/imag
    e/elephant.jpg
  • Reduced to 20 individuals in 1896
  • Now 30,000 individuals, with no detectable
    genetic diversity

17
Genetic Drift, Part B The founder effect
Change in allele frequencies when a new
population arises from only a few
individuals e.g., only a few fish are introduced
into a lake e.g., only a few birds make it to an
island
18
www.fishbase.org
Scorpaenidae Lionfish Pterois volitans
Founder Effect
  • New Atlantic population, maybe from only 10
    individuals

19
Gene Flow
addition or removal of alleles due to
individuals entering or leaving a population from
another population
20
  • On average, two humans differ by 0.1 (1 in 1000
    bp).
  • Is race a genetic reality?
  • NO 90 of genetic variation occurs within any
    single "race". LOTS OF OVERLAP
  • YES only 10 of the variation can be explained
    by Asian, African, or European origin.

21
Gene Flow
22
Bluefin Tuna
23
http//www.chambers-associates.org/Big-Marine-Fish
/map_bluefin_spawning_areas.html
24
Mutation
random, heritable changes in DNA that
introduces new alleles into a gene pool
25
random, heritable changes in DNA sequences that
introduce new alleles into a gene pool
Mutation
  • members.tripod.com/Alphacentaur/ X-men.JPG

26
Modes of natural selection
27
Modes of selection
28
Directional selection
Beak size selection in a Galápagos population of
the medium ground finch
29
Diversifying selection
30
Diversifying selection
Small bill size for soft seeds, large bills for
hard seeds selection against intermediate sized
bills which crack both types of seeds
inefficiently
31
Stabilizing selection
32
Stabilizing selection
http//www.hummingbirds.net/gallery0.html
33
What maintains genetic variation?
  • Diploidy
  • Balancing selection
  • Heterozygote advantage
  • Frequency-dependent selection
  • Neutral variation

34
Sicle cell anemia is a good example of
heterozygote advantage
35
Sex
36
The two-fold disadvantage of sex
BUT, genetic diversity allows adaptation to
changing environments
37
Sexual Selection
  • non-random mating where individuals have sexually
    dimorphic traits that make them more attractive
    to mates

Broad-billed hummingbirds
  • http//www.hummingbirds.net/

38
Sexual Selection - how can this be favored?
39
Sexual selection and the evolution of male
appearance
40
(No Transcript)
Write a Comment
User Comments (0)
About PowerShow.com