Microevolution - Troy High School

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Microevolution - Troy High School Powered By Docstoc
					          Introductory Questions #3
1)   When many diversely adapted species come from a common
     ancestor after being introduced to a new environment as we see
     with Darwin’s finches on the Galapagos Islands, this is
     called_________ ___________
2)   Name the two models that have been proposed to explain
     evolution observed in the fossil record. Which model (gradualism
     or punctuated equilibrium) is more reflective of the fossil record?
     Briefly explain why?
3)   How do new body designs and evolutionary novelties form?
4)   What is allometric growth and paedomorphosis?
5)   When was the last mass extinction event? How many have
     occurred in the last 600 million years? What typically occurs
     following a mass extinction event?
6)   Using the Geologic record on pg. 519 which era are we currently
     living in? Which period involved the emergence of flowering
     plants (angiosperms) and the extinction of dinosaurs?
   Ch. 23 Microevolution (Video)
1. How are Mosquito populations affected by genetic and
   environmental conditions
2. What affect did the insecticide have on the insects?
3. Which forms of isolation are presented in the last
4. What are some examples of species that are endemic to
   Catalina Island? How is inbreeding prevented for these

***Write the title for each segment and FIVE statements
   for each segment.
      Chapter 23-Microevolution
(Quantifying Evolution on a small scale)
      The Origin & History of Life (Ch. 26)
•   Age of the Earth (dating rocks)
•   Magnetic reversals
•   Plate tectonics (Continental Drift)
•   Miller’s Experiment (1953)- Abiotic synthesis of organic monomers
•   Clay surfaces serving as polymerization sites (Polymer formation)
•   Significance of RNA (as 1st genetic material)-Self-replicating molecules
•   Molecule packaging (“protobionts”)
•   Prokaryotes (heterotrophic)----Prokaryotes (autotrophic)
•   Stromatolites (Australia & Persian Gulf)
•   Reducing atmosphere changed to an oxidizing one
•   Endosymbiotic theory (prokaryotes engulf each other to form the 1st Eukaryote)
•   Multicellularity & Colonization
•   Importance of Mass Extinction Events (Permian & Cretaceous)
     – Meteor or Asteroid strike
     – Volcanic Activity
• Cambrian Explosion (Burgess shale)-540 mya
       Introductory Questions #4
1) Define what a gene pool is.
2) What are the three aspects in a population we
   examine in order to understand how evolution is
   occurring in a population.
3) If a population had 2500 individuals that are diploid,
   how many total alleles would be present?
4) In a population of 1000 humans, 840 possess the
   ability to roll their tongues (dominant trait) and 160
   cannot. Determine the frequency of the dominant and
   recessive alleles in the population.
5) What is happening if the population is in “genetic
6) What is the significance of the Hardy-Weinberg
• Small genetic changes in a
• Change in frequency of a single
  allele due to
                   Population genetics
• Population:
        a localized group of individuals
  belonging to the same species
• Species:
        a group of populations whose
  individuals have the potential to
  interbreed and produce fertile offspring
• Gene pool:
        the total aggregate of genes in a
  population at any one time
• Population genetics:
        the study of genetic changes in
• Modern synthesis/neo-Darwinism
    – Combining gene inheritance w/Nat.
• “Individuals are selected, but populations
         Hardy-Weinberg Principle
• States: frequencies of alleles & genotypes in a population’s
  gene pool remains constant from generation to generation.
• Model proposed in 1908
• Represents an ideal situation
• Seldom occurs in nature
• Mathematical model is used to compare populations
• Allows biologists to calculate allele frequencies in a
• Serves as a model for the genetic structure of a
     non-evolving population (equilibrium)
Represents “genetic equilibrium”
If the allele frequencies deviate from the predicted values of HW then
    the population is said to be evolving.
          Hardy-Weinberg Theorem
5 conditions for Equilibrium
-Very large population size
- No migration
- No net mutations
- Random mating
- No natural selection

**when all these are met then
  a population is not
            Hardy-Weinberg Equation
• p=frequency of one allele (A);   q=frequency of the other allele (a)
•                                  p+q=1.0
•   (p=1-q & q=1-p)
•   P2=frequency of AA genotype
•   2pq=frequency of Aa
•   q2=frequency of aa genotype;

           p2 + 2pq + q2 = 1.0
**Operates like a deck of cards: No matter
  how many times you shuffle the deck, the
  deck itself remains the same.
       Solving & Analyzing HW Principle
•    Problem: If you had 90 individuals that possessed the recessive
     condition in a population of 1000 individuals, determine the
     frequency of dominant and recessive alleles present in the
     population as well as the genotypic and phenotypic frequencies.
(1) Always start with the # of homozygous recessive alleles
 - aa = 90 and q2 = 90/1000 which is 0.09
 - a = square root of 0.09 which is 0.3
 - A = (1 – 0.3) which is 0.7
 - AA = (0.7) 2 which is 0.49

    - Aa = ???
    **Remember that p2 + 2pq + q2 = 1
                        (AA)   (Aa)    (aa)
• Involves small or minor changes in the allele frequencies
  within a population
• Five processes have been identified that change allele
   –   Nonrandom mating         (sexual selection)
   –   Gene flow                 (migration between populations)
   –   Genetic drift             (bottleneck effect & Founder effect)
   –   Mutations                 (unpredictable change in DNA)
   –   Natural selection         (differential reproduction)
        **certain alleles are favored over others in nature
A change in the gene pool
   of a population over a
   succession of
Genetic drift: changes
   in the gene pool of a
   small population due to
   chance (usually
   reduces genetic

     Two situations increase the impact of Genetic drift:
            **Bottleneck & Founder Effect

• The Bottleneck
  Effect: type of
  genetic drift resulting
  from a reduction in
  population (natural
  disaster) such that the
  surviving population is
  no longer genetically
  representative of the
  original population
           Bottleneck Effect
• Sudden change in the environment causing
  a shift in allele frequencies.
• Present Population does not reflect the
  original population
• Certain alleles become over represented
Ex. Elephant Seal Hunting (1890’s) were
  limited to just 20 individuals.
**Genetic Variation is reduced

• Founder Effect:
  2nd cause of genetic drift
  attributable to
  colonization by a
  limited number of
  individuals breaking off
  from a parent population

Gene Flow:
genetic exchange due to the
  migration of fertile
  individuals or gametes
  between populations
  (reduces differences
  between populations)
A Change in the DNA
 - source of new alleles
 - genetic variation
 - “raw materials of natural selection
 -unpredictable in nature
 -Doesn’t determine the direction of
 -causes small changes in allele
Approx. Mutation rate: One in every
   100,000 genes per generation
Nonrandom mating: inbreeding and assortive mating
 (both shift frequencies of different genotypes)
Mates are chosen according to desired characteristics
• Natural Selection:
  – Adapts a population to its environment
  – Accumulates and maintains FAVORABLE
    genotypes in a population
  – differential success in reproduction
  -only form of microevolution that adapts a
    population to its environment
  **recognizing Friends in a crowd.
            Natural selection
• Fitness: refers to the contribution an individual
   makes to the gene pool of the next generation
3 types of Selection:
• A. Directional
• B. Diversifying
• C. Stabilizing
          Three modes of Selection
• Stabilizing Selection:
  -well adapted to the environment
  -observed in many plants
  -selection eliminates extreme phenotypes
  -intermediate form is favored
• Directional Selection:
  -one phenotype extreme is favored
  -bell shaped curve is shifted (genetic drift)
  -Examples: Darwin’s Finches & Peppered moth
• Disruptive Selection:
  -causes divergence; splitting apart of the extreme phenotypes
  -extreme traits are favored
  -intermediate traits become elimanated
Three Types of Selection
      Natural Selection is the EMchanism
           of Adaptive Wvolution
• Selects only favorable phenotypic traits
• Unfavorable alleles are eliminated
• Can maintain genetic diversity
   – Polymorphism
   – Geographical variation
• Neutral Variations: offers no selective advantage or
  disadvantage Examples ??? (see pg. 468)
• Geographical variations and Clines (Clinal variation)
     **Observed in the common yarrow wildflower in the
            Sierra Nevada Mtns. (Pg. 464)
              Population Variation
• Polymorphism:
  coexistence of 2 or more
  distinct forms of
  individuals (morphs)
  within the same
• Geographical
  variation: differences in
  genetic structure between
  populations (cline)
           Balanced Polymorphism
Two or more alleles persist in a population over many
Preserved by:
•    Heterozygote advantage
    – Sickle cell anemia protests indiv. with malaria (pg. 466)
•      Frequency-dependent selection
    – Blue Jays locating & eating certain moths (pg. 467)
   Preserving Variations in a Population
Prevention of natural selection’s
   reduction of variation
   2nd set of chromosomes hides
   variation in the heterozygote
Balanced Polymorphism
   - heterozygote advantage (hybrid
   vigor; i.e., malaria/sickle-cell
   - frequency dependent selection
   (survival & reproduction of any 1
   morph declines if it becomes too
   common; i.e., parasite/host)
                    Sexual selection
• Sexual dimorphism:
  secondary sex
  characteristic distinction

• Sexual selection:
  selection towards
  secondary sex
  characteristics that leads
  to sexual dimorphism
       Introductory Questions #4
1) How can allele frequencies change in a population and
   increase variation? Give three examples. What do we
   call this when this is happening?
2) Does natural selection operate directly on the
   phenotype or genotype of organisms? Briefly explain
   your choice.
3) Name the three modes of selection. Explain how each
   mode is different and draw a graph representing each
4) Define what genetic polymorphism is and why
   balanced polymorphism is unique. Give the two
   mechanisms observed for balanced polymorphism.
5) What is a neutral variation? Give an example.
6) Which species do we see sexual dimorphism as means
   of mate selection

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