Chapter 23: Evolution of Population Flashcards

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1
Q

What is microevolution?

A
  • Change in allele frequencies in a population over generations
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2
Q

What are three mechanisms that cause allele frequency?

A
  1. Natural Selection (only one that causes adaptive evolution)
  2. Genetic Drift
  3. Gene flow

Adaptive Evolution: favor beneficial traits and eliminate harmful ones

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3
Q

What are the elements of Genetic Variation?

A
  • Caused by differences in genes
  • Phenotype: inherited genotype x environmental influences
  • Discrete characters (classified on either-or basis) & Quantitative characters (vary within a population) contribute to this
  • Measured as gene variability - avaerage heterozygosity (measures mean % of loci in the heterozygous population)
  • Also measured as nucleotide variability - comparing DNA sequences of pairs
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4
Q

What is geogrpahic variation in relation to genetic variation

A
  • Differences between gene pools of separate population
  • Ex: maderia home to several isolated populations of mice
  • Chromosomal variation among population is due to drift
  • Ex of geographic variation occuring is as a cline
  • Cline: graded change in a trait along a geographic axis
    - Ex: fish vary in a cold-adapative allele along a temp gradient
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5
Q

What are some sources of genetic variation?

A
  • Formation of new alleles: passing of mutation in nucleotide sequence of DNA
    - Point mutation: can be neutral, harmful, or benefical
    - Delete & rearrange mutation: typically harmful
    - Duplication: not as harmful
  • Rapid Reproduction: Mutation rates low in animals, plants, prokaryotes and high in viruses
  • Sexual Reporduction: recombination of existing alleles into new combinations helps produce genetic differenced making adaptation possible
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6
Q

What is the Hardy-Weinberg Equation’s importance?

A
  • Used to test whether a population is evolving
  • Population: localized group of individuals that can** interbreed** and produce fertile offspring
  • Gene pool: consists of all alleles for all loci in a population
  • Locus is fixed if population are homozygous for same allele
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7
Q

What are two ways that frequency for an allele in a population can be calculated?

A
  1. Diploid organisms: # of alleles at locus = total # of individuals times 2
  2. # of dominant alleles at a locus is 2 for each homozygous individual plus 1 allele for each heterozygous
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8
Q

Describe the Hardy-Weinberg equation in more detail

A
  • 2 alleles present at a locus
  • p + q = 1 (p is dominant and q is recessive)
  • p^2 + 2pq + q^2 = 1 (pq is heterozygous)
  • Describes a population that is NOT evolving (meets criteria meaning its is not evolving)
  • Principle: states that allelic frequencies and genotypes remain constant from generation to generation
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9
Q

What are the five conditions for nonevolving populations?

A
  1. No mutations
  2. Random mating
  3. No natural selection
  4. Extremly large population size
  5. No gene flow
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10
Q

How do you apply the Hardy-Weinberg Principle?

A

PKU: Locus that causes phenylketonuria
1. PKU gene mutation rate is low
2. Mate selection is random
3. Natural selection acts on just rare homozygous individuals
4. Population is large
5. Migration has no effect b/c other populations have similar allele frequencies

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11
Q

What are the elements of Genetic Drift?

A
  • Describes how allele frequencies fluctuate unpredictable from one generation to next
  • Effects: Genetic Drift…
    1. Significants in small populations
    2. Cause allele frequencies to change randomly
    3. Lead to loss of genetic variation in populations
    4. Causing harmful alleles to be fixed
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12
Q

What is the difference between Founder effect and Bottleneck effect?

A
  • Founder effect: few individuals become isolate from larger population
  • Bottleneck effect: sudden reduction in populaiton size due to change in environement (ex: human activity)
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13
Q

What is gene flow?

A
  • Movement of alleles among populations
  • Alleles transferred via movement of fetile individuals/gametes (ex: pollen)
  • Reduced variation over time
  • Increase fitness of population (ex: spread of alleles for resistance of insecticides increases fitness for mosquito population)
  • Important in evolutionary change in human populations
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14
Q

What are the elements of Natural Selection?

A
  • Differential success in reporudction: certain alleles being passed to next generation in greate proportions
  • Brings adaptive evolution via acting on phenotype
  • Relative fitness: contribution an indivudal makes to gene pool for next generation
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15
Q

What are the three modes of selection in relation to natural selection?

A
  1. Directional selection: **favors **individuals at one end of phenotypic range
  2. Disruptive selection: favors individuals at both ends of phenotypic range
  3. Stabilizing selection: acts against ends of phenotypic range, favors intermediate variants
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16
Q

What is the key role of Natural Selection in Adaptive Evolution?

A
  • Adaptation has risen by natural selection
  • Increases the frequencies of alleles that enhance survival reproduction
  • Adaptive evolution is a continuous process since environment constantly changes
  • Genetic Drift and gene flow increase/decrease match between organism and environment so it doesn’t consistently lead to adaptive evolution
17
Q

What is sexual selection?

A
  • Natural selection for mating success
  • Results in sexual dimorphism: marked differenced between sexes in secondary sexual characteristics (adam’s apple, facial hair, etc…)
  • Intrasexual selection: competition among individuals of often males for mates of the opp sex
  • Intersexual selection: often females are choosy in selecting their mates
18
Q

What are reasons why natural selection cannot fashion perfect organisms?

A
  1. Selection only happens in existing variations
  2. Evolution is limited
  3. Adaptation are often compromises
  4. Chance, natural selection, and environment interact
19
Q

What is neutral variation?

A

Genetic variation that doesn’t give a selective advantage or disadvantage

20
Q

What is Balancing Selection?

A
  • Occurs when natural selection maintains stable frequencies of two or more phenotypic forms
  • Includes:
    1. Heterozygote advantage: heterozygous have higher fitness
    2. Frequency-dependent selection: fitness of a phenotype declines when it becomes too common in a population