Chapter 11 Biology Textbook KEY CONCEPT HardyWeinberg equilibrium provides a framework for understanding how populations evolve HardyWeinberg equilibrium describes populations that are not evolving ID: 933884
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Slide1
Equilibrium, Speciation and Patterns in Evolution
Chapter 11 Biology Textbook
Slide2KEY CONCEPT
Hardy-Weinberg equilibrium provides a framework for understanding how populations evolve.
Slide3Hardy-Weinberg equilibrium describes populations that are not evolving.
Biologists use models to study populations.
Hardy-Weinberg equilibrium is a type of model.
Slide4Hardy-Weinberg equilibrium describes populations that are not evolving.
Genotype frequencies stay the same if five conditions are met.
very large population: no genetic drift no emigration or immigration: no gene flow no mutations: no new alleles added to gene poolrandom mating:no sexual selectionno natural selection:all traits aid equallyin survival
Slide5Hardy-Weinberg equilibrium describes populations that are not evolving.
Real populations rarely meet all five conditions.
Real population data iscompared to a model.Models are used tostudying how populationsevolve.
Slide6The Hardy-Weinberg equation is used to predict genotype frequencies in a population.
Predicted genotype frequencies are compared with actual frequencies.
used for traits in simple dominant-recessive systems
"The Hardy-Weinberg equation is based on Mendelian genetics. It is derived from a simple Punnett square in which p is the frequency of the dominant allele and q is the frequency of the recessive allele."
must know frequency of recessive homozygotes
p
2
+ 2pq + q
2
= 1
Slide7Five Factors that lead to Evolution
Genetic Drift
Genetic FlowMutationsSexual Selection
Slide8Genetic drift changes allele frequencies due to chance alone.
Slide9Gene flow moves alleles from one population to another.
Slide10Mutations produce the genetic variation needed for evolution.
Slide11Sexual selection selects for traits that improve mating success.
Slide12Natural selection selects for traits advantageous for survival.
Slide13In nature, populations evolve.
expected in all populations most of the time
respond to changing environments
Slide14The isolation of populations
can
lead to speciation. Populations become isolated when there is no gene flow. Isolated populations adapt to their own environments.Genetic differences can add up over generations.
Like with Darwin’s Finches
Slide15Reproductive isolation can occur between isolated populations.
members of different populations cannot mate successfully
final step to becoming separate species
Speciation is the rise of two or more species from one existing species.
Slide16Populations can become isolated in several ways.
#1 Behavioral
barriers can cause isolation.called behavioral isolationincludes differences in courtship or mating behaviors
Slide17#2 Geographic
barriers can cause isolation.
called geographic isolation
physical barriers divide population
Slide18Temporal Barriers
called temporal isolation
timing of reproductive periods prevents mating
Mule=horse + ass
Breeds in Jan-March in fast moving water
Breeds in late March-May in still water ponds
Slide19KEY CONCEPT
Evolution occurs in patterns.
Slide20Evolution through natural selection
is
not random.
Natural selection can have direction.
The effects of natural selection add up over time.
Slide21Convergent evolution describes evolution toward similar traits in unrelated species.
Slide22Divergent evolution describes evolution toward different traits in closely related species.
How do convergent and divergent evolution illustrate the directional nature of natural selection?
ancestor
red fox
kit fox
Slide23Species can shape each other over time.
Two or more species can evolve together through coevolution.
evolutionary paths become connectedspecies evolve in response to changes in each other
Bees and flowers
Yucca Moth & Yucca
Slide24Coevolution can occur in beneficial relationships.
Slide25Coevolution can occur in competitive relationships, sometimes called evolutionary.
Slide26Species can become extinct.
Extinction is the elimination of a species from Earth.
Background extinctions occur continuously at a very low rate.
occur at roughly the same rate as speciation
usually affects a few species in a small area
caused by local changes in environment
Slide27Background extinctions occur continuously at a very low rate.
occur at roughly the same rate as speciation
usually affects a few species in a small area
caused by local changes in environment
Passenger Pigeon
Slash and Burn
smallpox
Slide28Mass extinctions are rare but much more intense.
destroy many species at global level
thought to be caused by catastrophic events
at least five mass extinctions in last 600 million years
Slide29Speciation often occurs in patterns.
A pattern of punctuated equilibrium exists in the fossil record.
theory proposed by Eldredge and Gould in 1972episodes of speciation occur suddenly in geologic timefollowed by long periods of little evolutionary changerevised Darwin’s idea that species arose through gradual transformations
Slide30Many species evolve from one species during adaptive radiation.
ancestral species diversifies into many descendent species
descendent species
usually adapted to
wide range of
environments