Allele Frequencies _ Hardy Weinberg

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					    Allele
Frequencies,
  Types of
 Selection &
   Hardy-
  Weinberg
 What are the 2 Main Sources of Variation in
                Populations?

 Mutation- changes in DNA sequence
 Genetic Shuffling from Sexual Reproduction:
 During meiosis, chromosomes separate to form
 different gametes resulting in millions of
 different combinations. Also, crossing-over
 causes much more variety!
 Why Sex?
 http://www.pbs.org/wgbh/evolution/sex/index.html
Allele Frequencies Notes
      What is a GENE POOL?

A gene pool is
the combined
genetic
information of all
members of a
particular
population.
www.darwinawards.com
     What is relative frequency?
 The relative frequency of an allele is the
 number of times that allele occurs in a
 gene pool compared with the number of
 times other alleles occur.
 Expressed in percent.
    Relative Frequency Practice!
 In a population of 100 students, there are 40
  alleles for hitchhiker’s thumb and 60 alleles for a
  straight thumb. What is the relative frequency of
  alleles for hitchhiker’s thumb?
 40/100 = 0.40 = 40%

 What is the relative frequency of alleles for
  straight thumb?
 60/100 = 0.60 = 60%
    Allele frequencies of a population
                 change.
 The frequency of an allele in a
  gene pool of a population
  depends on many factors and
  may be stable or unstable over
  time. (CA Bio Standard)
 This is microevolution, which is
  the basis for macroevolution.
            How do allele
        frequencies change?

 Natural Selection!
 Natural selection acts on the phenotype
 rather than the genotype of an organism.
 (CA Bio Standard)
 Mutations!
 New mutations are constantly being
 generated in a gene pool. (CA Bio Standard)
 Natural Selection and Pesticides

 http://www.mhhe.com/biosci/esp/2001_gbio/folder_struct
  ure/ev/m2/s1/evm2s1_6.htm
     Allele Frequencies and
       Sickle Cell Anemia

Students know why alleles that
 are lethal in a homozygous
 individual may be carried in a
 heterozygote and thus
 maintained in a gene pool.
                A Mutation Story

http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html
1. What is the name of the deadly disease?

2. What causes Malaria?

3. How is having one mutated gene beneficial to Africans?

4. How many genes does an individual need to have to express sickle cell
   anemia?
5. How can a mutation be harmful in one environment and helpful in
   another?
6. Why would a mutation persist if it kills people?

7. Why are there more people with sickle cell anemia in one part of the
   world than in other parts?
Allele Frequency and Sickle Cell
   Anemia Background Info

        Read popcorn style!
              March 22

 Warm-Up: Explain sickle cell anemia.
        How Sickle Cell Works

 http://www.youtube.com/watch?v=9UpwV1tdxcs&feature
  =related
          Sickle Cell and Pain

 http://www.youtube.com/watch?v=1fSKrUOwL9c&featur
  e=related
Malaria Infects Red Blood Cells

 http://www.youtube.com/watch?v=F_Xi3hnhtbg&feature
  =related
Allele Frequency and Sickle Cell
          Anemia Lab
          March 31

Warm-Up: Why are alleles that are
lethal in a homozygous individual
maintained in the gene pool? (Use
Sickle Cell and Malaria as an
example.)
            LEARNING LOG 1

 Paste the half sheet, How to Keep a Learning Log to the
  back page of your notebook.

 Write LEARNING LOG 1: DARWIN,
  NATURAL SELECTION AND CHANGES
  IN ALLELE FREQUENCIES on the next
  free page of your notebook. Complete
  the learning log. (15 points)
Types of Selection Notes
       (Ch. 16.2)
    In Single- Gene Traits,

… there are two phenotypes,
 whereas in polygenic traits,
 there are multiple phenotypes.
 Natural Selection acts
 differently on each of these.
  Is height a
 single-gene
   trait or a
  polygenic
     trait?

Polygenic Trait!
Is Sickle Cell Anemia a single gene
      trait or a polygenic trait?




                      Single
                      Gene Trait!
Natural Selection on Single-Gene
      Traits can lead to…

…changes in allele frequencies and
 therefore, evolution!
 This was shown in the Peppered
 Moth Simulation.
Natural Selection on Polygenic
 Traits occurs in three ways:

1. Disruptive Selection

2. Stabilizing Selection

3. Directional Selection
Directional Selection


  When individuals at one end of the
   curve have a higher fitness than those
   at the other end.
  Examples: Finch bills, peppered moths
 Animation of Directional Selection:

  http://wps.prenhall.com/wps/media/objects/487/499541/C
   DA22_2/CDA22_2b/CDA22_2b.htm
  Stabilizing Selection


 When individuals near the center of the curve
  have higher fitness than individuals at either
  end of the curve- selection against both
  extremes.
 Examples: human baby size, lizard size, number of
  children
Animation of Stabilizing Selection:
 http://wps.prenhall.com/esm_freeman_biosci_1/0,6452,499573-
  ,00.html
          Disruptive
          Selection

 When individuals at the lower and upper ends
  of the curve have higher fitness than those in
  the middle. This could cause the population to
  split into two distinct subgroups.
 Examples: duck bills, sexual dimorphism, sickle
  cell anemia
Animation of Disruptive Selection:

 http://wps.prenhall.com/wps/media/objects/487/499541/CDA22_2/
  CDA22_2d/CDA22_2d.htm
  Sexual dimorphism: Males and females of the
same species look noticeably different from each
                     other
This is caused by sexual
selection, which acts on an
organism's ability to obtain
(often by any means
necessary!) or successfully
copulate with a mate.
             Sexual Selection
 Sexual selection and natural selection may often operate
  in opposing directions.

 Males, who usually compete for mates, have traits such as
  showy plumage in spite of their potential costs, such as
  increased visibility to predators, and attacks from rival
  males.
           APRIL 1st

WARM-UP: Do you think evolution can
occur in ways other than natural
selection? Explain why or why not.
           Your Ideas:

No, only through Natural
 selection
Yes: Artificial Selection
Yes: randomly
Yes: what if there’s a natural
 disaster…
 Can evolution happen in ways
                                 YES!
 other than Natural Selection?
 Genetic Drift is
  random change in
  allele frequencies in
  small populations.
 It can cause
  evolution due to
  chance rather than
  natural selection.
    Genetic Drift causes…

the founder effect- when a
 migration of a small subgroup
 of a population causes a
 change in allele frequencies.
           Agile Mind Website
 Go to the website:
 http://lausd7.agilemind.com
 Type in your username and password.

 Go to Mechanisms for Evolution, then
 Exploring, then Other mechanisms of
 evolution.
 Go through the reading and animations.

 Take the assessment at the end.
CA BIO STANDARD- Evolution

Students know the conditions
 for Hardy-Weinberg
 equilibrium in a population and
 why these conditions are not
 likely to appear in nature.
      Hardy-Weinberg Principle
 Allele frequencies in a population will
  remain constant unless one or more factors
  causes those frequencies to change.
 When allele frequencies remain constant, it is
  called genetic equilibrium.
 If there is genetic equilibrium, evolution will not
  occur.
 Five conditions required to
maintain genetic equilibrium:

1. Random mating
2. Large population
3. No movement into or out of the
   population
4. No mutations
5. No natural selection
  Conditions necessary for Hardy
      Weinberg Equilibrium
 http://www.phschool.com/science/biology_place/labbench
  /lab8/intro.html
 Animation of H-W Conditions

 http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flas
  h/life4e_15-6-OSU.swf
  Hardy Weinberg Equation

Students know how to solve the
 Hardy-Weinberg equation to
 predict the frequency of
 genotypes in a population, given
 the frequency of phenotypes.
   Hardy Weinberg Equation

 Frequency of dominant allele = p
 Frequency of recessive allele = q
 The sum of the two alleles in a
 population = 100%
                   or…
                         p+q=1
   Hardy Weinberg Equation

              p2 + 2pq + q2 = 1
 p2 = frequency of AA homozygotes
 2pq = frequency of Aa heterozygotes
 q2 = frequency of aa homozygotes
 1 = frequency of all genotypes
Hardy Weinberg Sample Problems

 http://www.phschool.com/science/biology_place/labbench
  /lab8/samprob1.html
  H-W Sample Problem: Albinism

 http://anthro.palomar.edu/synthetic/sample.htm
Hardy Weinberg Problem Set

         15 points

				
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