chapter12_Biology Powerpoint

Processes of Evolution

Chapter 12

Part 1

12.1 Impacts/IssuesRise of the Super Rats

When humans tried to eradicate rats with warfarin, natural selection favored individuals with a mutation for warfarin resistance

Video: Rise of the super rats

12.2 Making Waves in the Gene Pool

Individuals in a population share the same traits (phenotype) because they share the same genes (genotype)

Gene pool • All of the genes in a population

Alleles and Traits

Alleles of the same genes are the main source of variation in a population• Traits with two distinct forms are dimorphic• Traits with several distinct forms are polymorphic• Traits with continuous variation may have

interactions of several genes or be influence by environment

Mutation is the source of new alleles

Sources of Variation in Traits

Phenotypic Variation in Humans

Mutation Revisited

Mutations are the original source of alleles, but many are lethal or neutral

Lethal mutation • Mutation that drastically alters phenotype; usually

causes death

Neutral mutation • A mutation that has no effect on survival or

reproduction

Allele Frequencies

Microevolution (change in allele frequencies) is always occurring in natural populations

Microevolution • Small-scale change in allele frequencies of a

population or species

Allele frequency • Abundance of a particular allele among members

of a population

Genetic Equilibrium

Genetic equilibrium • Theoretical state in which a population is not

evolving (allele frequencies do not change)

Only occurs if five conditions are met:• Mutations never occur, population is infinitely

large, population is isolated from gene flow, mating is random, all individuals survive and reproduce equally

Processes of Microevolution

Genetic equilibrium does not occur in nature because processes that drive microevolution are always in play• Mutation• Natural selection• Genetic drift• Gene flow

Animation: Adaptation to what?

Animation: How to find out if a population is evolving

Animation: Sources of genotype variation

12.3 Natural Selection Revisited

Natural selection occurs in different patterns depending on species and selection pressures • Directional selection• Stabilizing selection • Disruptive selection

Directional Selection

Directional selection • Mode of natural selection in which phenotypes at

one end of a range of variation are favored• Allele frequencies shift in a consistent direction in

response to selection pressure

Examples: peppered moths, rock pocket mice, antibiotic-resistant bacteria

Directional Selection

Fig. 12-3, p. 219

Fig. 12-3a, p. 219

Fig. 12-3a, p. 219

Time 1N

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Range of values for the trait

Fig. 12-3b, p. 219

Fig. 12-3b, p. 219

Time 2

Fig. 12-3c, p. 219

Fig. 12-3c, p. 219

Time 3

Animation: Directional selection

Directional Selection in Peppered Moths

Predation pressure favors moths that are best camouflaged when the environment changes

Fig. 12-4, p. 219

Fig. 12-4a, p. 219

Fig. 12-4b, p. 219

Fig. 12-4c, p. 219

Fig. 12-4d, p. 219

Directional Selection in Rock Pocket Mice

Mice with coat colors that do not match their surroundings are more easily seen by predators

Stabilizing Selection

Stabilizing selection • Mode of natural selection in which intermediate

phenotypes are favored and extreme forms are eliminated

Example: sociable weavers

Stabilizing Selection

Fig. 12-6, p. 221

Fig. 12-6a, p. 221

Fig. 12-6a, p. 221

Nu

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Time 1

Range of values for the trait

Fig. 12-6b, p. 221

Fig. 12-6b, p. 221

Time 2

Fig. 12-6c, p. 221

Fig. 12-6c, p. 221

Time 3

Animation: Stabilizing selection

Stabilizing Selection in Sociable Weavers

Body weight in sociable weavers is a trade off between starvation and predation

Fig. 12-7, p. 221

Fig. 12-7a, p. 221

Fig. 12-7b, p. 221

Fig. 12-7b, p. 221

300

200

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23.5

25.5

27.5

29.5

31.5

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Body mass (grams)

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Disruptive Selection

Disruptive selection • Mode of natural selection that favors extreme

phenotypes in a range of variation• Intermediate forms are selected against

Example: African seedcrackers

Disruptive Selection

Fig. 12-8, p. 222

Fig. 12-8a, p. 222

Fig. 12-8a, p. 222

Nu

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Range of values for the trait

Fig. 12-8b, p. 222

Fig. 12-8b, p. 222

Time 2

Fig. 12-8c, p. 222

Fig. 12-8c, p. 222

Time 3

Animation: Disruptive selection

Disruptive Selectionin African Seedcrackers

African seedcrackers tend to have either a large bill or a small one – but no sizes between

Fig. 12-9a, p. 222

Fig. 12-9a, p. 222lower bill 12 mm wide

Fig. 12-9b, p. 222

Fig. 12-9b, p. 222

lower bill 15 mm wide

Animation: Change in moth population

Animation: Disruptive selection among African finches