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Genetic Variation

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Genetic Variation & Evolution Chapter 23 What you need to know! How mutation and sexual reproduction each produce genetic variation Variation Variations exist between ... – PowerPoint PPT presentation

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Title: Genetic Variation


1
Genetic Variation Evolution
  • Chapter 23

2
What you need to know!
  • How mutation and sexual reproduction each produce
    genetic variation

3
Variation
  • Variations exist between individuals in a given
    population. The following are heritable
  • Mutation mostly point mutations (other
    mutations are possible)
  • Sexual Reproduction crossing over, independent
    assortment
  • Diploidy recessive alleles can be hidden (from
    natural selection) but stay around

4
Variation
  • Outbreeding mating with non-related partners
    increases new allele combinations
  • Behavioral incest is blocked in most higher order
    species
  • Balanced polymorphism different phenotypes in a
    single population propagate natural selection
  • Heterozygous advantage advantage to
    heterozygous alleles despite deadly recessive
    alleles (ex. Sickle cell anemia)

5
Variation
  • Hybrid Vigor superior quality of offspring when
    crossing highly inbred strains
  • Frequency dependent selection predators form
    search images fitting most common prey
    phenotypes
  • http//evolution.berkeley.edu/evolibrary/article/h
    appyface_11
  • Neutral Variation no selection pressure for
    certain phenotypes
  • Silent Mutations mutations that do not impact
    phenotypes (no selection pressure)

6
Natural Selection
  • Differential reproductive success of different
    phenotypes as a result of the interaction with
    the environment
  • Due to genetic variations certain phenotypes are
    better or worse adapted
  • Survival depends on the adaptations (fitness)
  • Reproduction depends on survival

7
Microevolution
  • Def Natural selection causes changes in
    relative frequencies of alleles in the gene pool
    (Hardy Weinberg)
  • Adaptation means genes are selected to
  • Increase (good)
  • Decrease (bad)
  • Stay the same (neutral)
  • Evolution is the accumulation of advantageous
    traits

8
Stabilizing Selection
  • Extreme phenotypes are bad adapatations
  • Example primate birth weight
  • Too small and the baby dies
  • Too large and the mother dies
  • Draw

9
Directional Selection
  • A single extreme adaptation is good
  • Example peppered moths
  • Draw

10
Diversifying Selection
  • Selection against the common phenotype
  • Selection for both extremes
  • Example weeds are either very tall (difficult
    to uproot) or very short (survive lawn mowers)

11
Sexual Selection
  • Selection for sexual phenotypes
  • Male competition fittest male mates most
    (antlers, horns, body size)
  • Female choice attractiveness and mating
    behavior
  • Sexual dimorphism diifferent appearance of
    males and females in certain species

12
Artificial Selection
  • Directional selection carried out by humans
  • Humans select a desireable trait and only breed
    animals with the selected trait (dogs, cats,
    sheep, horses, cows, etc.)

13
Imperfection
  • Natural selection does not fashion the perfect
    organism because
  • Selection only edits existing variation
  • Evolution is limited by historical constraints
  • Adaptations are often compromises
  • Change, natural selection and the environment
    interact

14
Homework
  • Concept Checks 23.1 (pg. 458)
  • What did Mendels findings about genetics add to
    Darwins theory of evolution by natural
    selection?
  • Suppose a population or organisms with 500 gene
    loci is fixed at half of these loci. How many
    alleles are found in its gene pool? Explain.
  • Which parts of the Hardy-Weinberg equation (p2
    2pq q2 1) correspond to the frequency of
    individuals that have at least one PKU allele?

15
Homework
  • Concept Checks 23.2 (pg. 460)
  • Of all the mutations that occur, why do only a
    small fraction become widespread in a gene pool?
  • How does sexual recombination produce variation?

16
Homework
  • Concept Checks 23.3 (pg. 462)
  • In what sense is natural selection more
    predictable than genetic drift?
  • Distinguish genetic drift and gene flow in terms
    of (a) how they occur and (b) their implications
    for future genetic variation in a population.

17
Homework
  • Concept Checks 23.4 (pg. 470)
  • Does nucleotide variability in a population
    always correspond to phenotypic polymorphism?
    Why or why not?
  • What is the relative fitness of a sterile mule?
    Explain.
  • How does sexual selection lead to sexual
    dimorphism?
  • Explain what is meant by the reproductive
    handicap of sex.
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