microevolution vs. macroevolution microevolution: survival through the inheritance of favorable...
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MICROEVOLUTION MICROEVOLUTION VS. VS. MACROEVOLUTIONMACROEVOLUTION
• Microevolution: survival through the inheritance of favorable characteristics – mutations – selection
• Macroevolution: progression of biodiversity through geological time – speciation – extinction
MICROEVOLUTIONMICROEVOLUTION
Evolutionary Mechanisms
Types of Natural Selection
Hardy-Weinberg Equilibrium
WHAT IS WHAT IS MICROMICROEVOLUTION?EVOLUTION?
• Traces generational changes in a population of organisms
• Changes eh?– Allelic frequency changes within a
gene pool!
•
WHAT LEADS TO CHANGES WHAT LEADS TO CHANGES IN THE GENE POOL OF A IN THE GENE POOL OF A
POPULATION?POPULATION?• SMALL POPULATION SIZE
(small pop frequencies)
toss a coin to prove it.
MECHANISMS OF MECHANISMS OF EVOLUTIONEVOLUTION
• GENETIC DRIFT
(random/chance events that change the gene pool of a small population)
examples:
natural disasters
2 TYPES OF GENETIC DRIFT 2 TYPES OF GENETIC DRIFT MECHANISMSMECHANISMS
• Genetic Bottleneck
dramatic decrease in pop size due to :
catastrophes
predation
disease, etc.
• Founder Effectmigration leads to changes in allele
frequencies from population of origin
WHAT ELSE CAUSES GENE WHAT ELSE CAUSES GENE POOL CHANGES ?POOL CHANGES ?
• GENE FLOW
immigration
emigration
EX OF GENE FLOW IN EX OF GENE FLOW IN HUMANSHUMANS
• Frequency of Rh- allele among Africans:
63%
• Frequency of Rh- allele among
African-Americans
45%
• Frequency of Rh- allele among White European population
3%
• MUTATIONS
may produce a selective advantage
may produce deleterious effects
may be harmless
• NATURAL SELECTION!
increases/decreases allele frequencies due to environmental impact.
Ex: English Peppered Moths
• NON-RANDOM MATING
individuals choose based upon traits
(vertebrates)
individuals “choose” based upon
physical proximity
(invertebrates)
OTHER FORMS OF NON-OTHER FORMS OF NON-RANDOM MATING:RANDOM MATING:
• INBREEDING– Proximity issues
• SEXUAL SELECTION:1. Male competition:
# offspring fitness2. Female choice: quality offspring fitness
SEXUAL SEXUAL SELECTIONSELECTION
Picky females, show-off males…
MICROEVOLUTION REVIEWMICROEVOLUTION REVIEW
• Changes in the GENE POOL!
• Caused by:– Gene Flow– Natural Selection – Mutations– Non-Random Mating
• Sexual Selection• Inbreeding
THE SIGNIFICANCE OF THE SIGNIFICANCE OF SELECTIONSELECTION
• Selection increases the adaptive qualities of a population for the environment in which it lives.Types of Selection:
Natural Selection determined by phenotype selection toward phenotypes that
improve fitness
SUBDIVISIONS OF NATURAL SUBDIVISIONS OF NATURAL SELECTION…SELECTION…
Stabilizing Selection
Eliminates individuals with extreme traits. Results in decreased variation
Directional Selection
Favors traits at ONE extreme
ex: resistance to insecticides
DIRECTIONAL SELECTIONDIRECTIONAL SELECTION
Disruptive Selection
Selection toward BOTH extremes. Extreme traits are favored, common traits are NOT!
Results in major divisions in population!
What might result?
DISRUPTIVE SELECTIONDISRUPTIVE SELECTION
ARTIFICIAL ARTIFICIAL SELECTIONSELECTION
Directional selection determined by humans
CAUSES OF VARIATIONCAUSES OF VARIATION
• Mutation is the ultimate source of variation
• Two major types of mutations:–Gene mutations
–Chromosome mutations
GENE MUTATIONSGENE MUTATIONS
Addition / Insertion
Deletion
Substitution
Inversion
SPECIFIC EXAMPLES OF SPECIFIC EXAMPLES OF MUTATIONSMUTATIONS
• Gene mutations–PKU (phenylketonuria)
–CF (cystic fibrosis)
• Chromosome mutation–Klinefelter syndrome (male with
47,XXY karyotype)
ONCE MUTATIONS HAVE ONCE MUTATIONS HAVE ARISEN, FURTHER ARISEN, FURTHER
VARIATION RESULTS FROM:VARIATION RESULTS FROM:• Recombination of
alleles during meiosis
• Recombination of alleles during fertilization
ONCE GENETIC ONCE GENETIC VARIATION HAS ARISEN, VARIATION HAS ARISEN,
THERE IS ALSO THERE IS ALSO PHENOTYPIC VARIATION.PHENOTYPIC VARIATION.
• Recall that, according to Darwin’s Theory, due to competition within populations, there is …
Differential Reproduction of Selected Phenotypes
GREAT EXAMPLE OF GREAT EXAMPLE OF DIFFERENTIAL DIFFERENTIAL
REPRODUCTION OF REPRODUCTION OF SELECTED PHENOTYPES:SELECTED PHENOTYPES:
ULTIMATE RESULT OF ULTIMATE RESULT OF EVOLUTIONEVOLUTION
Change in the genetic composition (gene pool) of a
population.
RELATED CAUSES OF RELATED CAUSES OF GENETIC VARIATIONGENETIC VARIATION
Sexual Reproduction!
• Diploidy
• Outbreeding
MINORITY ADVANTAGE…MINORITY ADVANTAGE…
• 50/50 Sex Ratio
• Predation (more common phenotype preferred by predator)
• The Lefty Hypothesis
10-15 % general population
>50% contact sports (esp. males)
REPRODUCTIVE ISOLATIONREPRODUCTIVE ISOLATION
Prezygotic
• Temporal isolation
• Behavioral isolation
• Mechanical isolation
• Ecological isolation
• Gametic isolation
Postzygotic
• Hybrid inviability
• Hybrid sterility
• Hybrid breakdown
ALLOPATRIC SPECIATIONALLOPATRIC SPECIATION
SYMPATRIC SPECIATIONSYMPATRIC SPECIATION
GRADUALISMGRADUALISM
Species A evolves to become species B.
LONG, GRADUAL process!
PUNCTUATED PUNCTUATED EQUILIBRIUMEQUILIBRIUM
• Evolution is Slow with brief periods of rapid development of new species.
THE HARDY WEINBERG LAWTHE HARDY WEINBERG LAW
• If allele frequencies for a population do not change…
NO EVOLUTION IS OCCURRING!
• Genetic Equilibrium
• Hardy Weinberg Equilibrium
GENETIC EQUILIBRIUM GENETIC EQUILIBRIUM OCCURS ONLY IF THERE IS…OCCURS ONLY IF THERE IS…
1.A large breeding population 2.Random mating 3.No change in allelic frequen
cy due to mutation
4.No immigration or emigration
5.No natural selection
EQUILIBRIUM REQUIRES…EQUILIBRIUM REQUIRES…
• Large Population Size(laws of probability must apply)
• Isolation of Population(no immigration/emigration to/from other populations)
• NO MUTATIONS ALLOWED!• NO NATURAL SELECTION ! all traits must be selectively neutral• Mating Must Be RANDOM equal probabilities of mating btwn genotypes
IS HW EQUILIBRIUM IS HW EQUILIBRIUM POSSIBLE?POSSIBLE?
• YES ? / NO ?
• WHY / WHY NOT??
• http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf
THE HARDY-WEINBERG THE HARDY-WEINBERG EQUATIONEQUATION
• Given one locus with two alleles (A,a) the frequency of either allele is described by a number from zero to one:
allele absent from pop freq = 0
same allele in all indiv in pop
freq = 1
WHAT IF BOTH ALLELES ARE WHAT IF BOTH ALLELES ARE PRESENT IN A POPULATION?PRESENT IN A POPULATION?• Frequency of both alleles is equal to
p + q = 1
[p = dominant allele (A)]
[q = recessive allele (a)]
• Knowing the frequency of one allele allows for the calculation of the other…
p = 1- q ; q = 1 - p
• If p+q=1,
then (p+q)2 = 1.
Expand it and get…
p 2 + 2pq + q2 = 1
WHAT DOES IT ALL MEAN WHAT DOES IT ALL MEAN GENOTYPICALLY?GENOTYPICALLY?
p2 = frequency of AA
2pq = frequency of Aa
q2 = frequency of aa
PROBLEM 1PROBLEM 1
• In pigs, the allele for black coat (b) is recessive to the allele for pink coat (B).
WHAT % OF PIGS ARE WHAT % OF PIGS ARE HETEROZYGOUS FOR PINK HETEROZYGOUS FOR PINK
COAT?COAT?
PROBLEM 2PROBLEM 2In a certain population of 1000 fruit flies, 640 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color?
PROBLEM 3PROBLEM 3
Phenylketonuria (PKU) is a human metabolic disorder that results in mental retardation if it is untreated in infancy. In the United States, one out of approximately 10,000 babies is born with the disorder. Approximately what percent of the population are heterozygous carriers of the recessive PKU allele?
IF 9% OF AN AFRICAN IF 9% OF AN AFRICAN POPULATION IS BORN POPULATION IS BORN
WITH A SEVERE FORM OF WITH A SEVERE FORM OF SICKLE-CELL ANEMIA (SS), SICKLE-CELL ANEMIA (SS),
WHAT PERCENTAGE OF WHAT PERCENTAGE OF THE POPULATION WILL BE THE POPULATION WILL BE
MORE RESISTANT TO MORE RESISTANT TO MALARIA BECAUSE THEY MALARIA BECAUSE THEY ARE HETEROZYGOUS(SS) ARE HETEROZYGOUS(SS)
FOR THE SICKLE-CELL FOR THE SICKLE-CELL GENE?GENE?