11.3 other mechanisms of evolution key concept natural selection is not the only mechanism through...
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11.3 Other Mechanisms of Evolution
KEY CONCEPT Natural selection is not the only mechanism through which populations evolve.
11.3 Other Mechanisms of Evolution
NGSSS
•SC.912.L.15.14* Discuss mechanisms of evolutionary change other than natural selection such as genetic drift and gene flow. (MODERATE)
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
1.1. MutationMutation:: fundamental origin of fundamental origin of allall genetic (DNA) change.genetic (DNA) change.
1.1. MutationMutation:: fundamental origin of fundamental origin of allall genetic (DNA) change.genetic (DNA) change.
Crossing-overCrossing-overCrossing-overCrossing-over
……others at grosser others at grosser chromosome levelchromosome level……others at grosser others at grosser chromosome levelchromosome level
11.3 Other Mechanisms of Evolution
Gene flow is the movement of alleles between populations.
• Gene flow occurs when individuals join new populations and reproduce.
• Gene flow keeps neighboring populations similar.
• Low gene flow increases the chance that two populations will evolve into different species.
This map shows the locations where young banded eagles were found during the first summer after hatching
11.3 Other Mechanisms of Evolution
Genetic drift is a change in allele frequencies due to chance.
• Genetic drift causes a loss of genetic diversity.• It is most common in small populations.• A population bottleneck can lead to genetic drift.
– It occurs when an eventdrastically reducespopulation size.
– The bottleneck effect isgenetic drift that occursafter a bottleneck event.
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations accumulate isolated populations accumulate different mutations over time.different mutations over time.
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations accumulate isolated populations accumulate different mutations over time.different mutations over time.
In a continuous In a continuous population, genetic population, genetic novelty can spread novelty can spread locally.locally.
In a continuous In a continuous population, genetic population, genetic novelty can spread novelty can spread locally.locally.
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations isolated populations accumulate different mutations over time.accumulate different mutations over time.
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations isolated populations accumulate different mutations over time.accumulate different mutations over time.
Local spreading of allelesLocal spreading of allelesLocal spreading of allelesLocal spreading of alleles
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations isolated populations accumulate different mutations over time.accumulate different mutations over time.
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations isolated populations accumulate different mutations over time.accumulate different mutations over time.
Local spreading of allelesLocal spreading of allelesLocal spreading of allelesLocal spreading of alleles
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations accumulate isolated populations accumulate different mutations over time.different mutations over time.
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift:: isolated populations accumulate isolated populations accumulate different mutations over time.different mutations over time.
Spreading process Spreading process known as ‘known as ‘gene gene flowflow’.’.
Spreading process Spreading process known as ‘known as ‘gene gene flowflow’.’.
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
But in But in discontinuousdiscontinuous populations, populations, gene gene flow flow is blocked.is blocked.
But in But in discontinuousdiscontinuous populations, populations, gene gene flow flow is blocked.is blocked.
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
Variations Variations accumulate without accumulate without inter-demicinter-demic exchange exchange
Variations Variations accumulate without accumulate without inter-demicinter-demic exchange exchange
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
Of course, this Of course, this works at many loci works at many loci simultaneouslysimultaneously
Of course, this Of course, this works at many loci works at many loci simultaneouslysimultaneously
11.3 Other Mechanisms of Evolution
• The founding of a small population can lead to genetic drift.
– It occurs when a few individuals start a new population.– The founder effect is genetic drift that occurs after start
of new population.
11.3 Other Mechanisms of Evolution
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Founder Effect.--
Human example: your tribe had to Human example: your tribe had to live near the Bering land bridge…live near the Bering land bridge…
11.3 Other Mechanisms of Evolution
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Founder Effect.--
……to invade & settle the ‘New World’!to invade & settle the ‘New World’!
11.3 Other Mechanisms of Evolution
• Genetic drift has negative effects on a population.
– less likely to have some individuals that can adapt – harmful alleles can become more common due to
chance
11.3 Other Mechanisms of Evolution
Sexual selection occurs when certain traits increase mating success.
• Sexual selection occurs due to higher cost of reproduction for females.– males produce many
sperm continuously– females are more
limited in potential offspring each cycle
11.3 Other Mechanisms of Evolution
• There are two types of sexual selection.
– intrasexual selection: competition among males– intersexual selection: males display certain traits to
females
11.3 Other Mechanisms of Evolution
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Four causes of evolutionary change:Four causes of evolutionary change:
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift: isolation : isolation accumulation of accumulation of mutations mutations
3.3. Founder EffectFounder Effect: immigrant sampling bias. : immigrant sampling bias.
4.4. Natural SelectionNatural Selection: reproductive race: reproductive race
These 4 interact synergisticallyThese 4 interact synergistically
1.1. MutationMutation: fundamental genetic shifts.: fundamental genetic shifts.
2.2. Genetic DriftGenetic Drift: isolation : isolation accumulation of accumulation of mutations mutations
3.3. Founder EffectFounder Effect: immigrant sampling bias. : immigrant sampling bias.
4.4. Natural SelectionNatural Selection: reproductive race: reproductive race
These 4 interact synergisticallyThese 4 interact synergistically