Learning Target: Evolution of Populations
Ch. 11.1 – 11.2, pp. 329 – 333, & Ch. 11.6, pp. 347 - 351
I Can…Describe how
genetic variation within a
population increases the
chance that some individuals
will survive and describe
different mechanisms of
evolution.
Genetic Variation Within Populations
Ch. 11.1, pp. 328-329
Key Concept:
• Populations share a common gene pool
Main Ideas:
• Genetic variation within a population
increases the chance that some individuals
will survive.
• Genetic variation comes from
• Mutation
• Recombination
Genetic Variation Within Populations
Ch. 11.1, pp. 328-329
Gene pool
• Store of population’s genetic variation
• All alleles within population
Allele frequency
• Measure of how common a certain allele is
within the population
• Each autosomal gene has two alleles
• Homozygous
• Heterozygous
Genetic Variation Within Populations
Ch. 11.1, pp. 328-329
Phenotype traits:
• Monogenic or polygenic
• Dominant/Recessive
• Incomplete Dominance
• Co-Dominance
• Permissive/Epistasis
Genetic Variation Within Populations
Ch. 11.1, pp. 328-329
Allele Variation:
• Mutations
• Change in DNA nucleotide sequence
• Recombination
• New different combinations of alleles
• Crossing over during meiosis
Genetic Variation Within Populations
Ch. 11.1, pp. 328-329
Allele frequency in a population gene pool can
be calculated.
Natural Selection in Populations
Ch. 11.2, pp. 330-333
Key Concept:
• Populations, not individuals, evolve
Main Ideas:
• Natural selection
•
•
Acts on distribution of traits
Can change the distribution of traits in one of three
ways
• Microevolution
•
Observable change in allele frequency of a population
over time
Natural Selection in Populations
Ch. 11.2, pp. 330-333
Normal Distribution
• Phenotype frequency
highest at mean
• Decreases as nears
extremes
• “Bell” shaped curve
• Not undergoing
selective pressure
Natural Selection in Populations
Ch. 11.2, pp. 330-333
Directional Selection
• Favors one of the extreme phenotypes
• Causes shift of highest allele frequency
from mean towards one extreme
Natural Selection in Populations
Ch. 11.2, pp. 330-333
Stabilizing Selection
• Favors mean phenotype
Natural Selection in Populations
Ch. 11.2, pp. 330-333
Disruptive Selection
• Favors both extreme phenotypes
• Selects against mean phenotype
Natural Selection in Populations
Ch. 11.2, pp. 330-333
Remember:
Direction of Evolution ≠ Purpose or Intent
Patterns in Evolution
Ch. 11.6, pp. 347-351
Key Concept:
• Evolution occurs in patterns
Main Ideas:
• Evolution is not random
• Species can shape each other over time
• Species can become extinct
• Speciation often occurs in patterns
Patterns in Evolution
Ch. 11.6, pp. 347-351
Evolution occurs in patterns
•
Evolution through natural selection is NOT
random.
•
Mutations cannot be predicted accurately
• Termed “Random event”
• Source of genetic variation
• Natural selection acts upon the variation
• Not random
• Selective pressure makes one variation more
advantageous in survival and/or reproduction
than other variation
Patterns in Evolution
Ch. 11.6, pp. 347-351
Selective pressures act upon variations in
population:
•
Adds up over many generations
•
Advantageous variation becomes more prevalent in
population over time.
• Population becomes “adapted”
• The adaptation (advantage variation) becomes more
prevalent and allele frequencies change.
Direction of Evolution ≠ Purpose or Intent
Patterns in Evolution
Ch. 11.6, pp. 347-351
Environment drives natural selection
• Environments can change
• Convergent Evolution
•
Different species must adapt to similar environmental
pressures.
• Evolution toward similar characteristics in unrelated
species
• Analogous structures
• e.g. dolphin and shark tail fin
Patterns in Evolution
Ch. 11.6, pp. 347-351
• Divergent Evolution
•
Closely related species evolve in different
direction and become increasingly different
•
•
Common ancestor
Homologous structures
• e.g. Kit fox & Red fox, Galapagos finches, Grey
wolf to domestic dogs
Question: Both turtles and snails have shells. Is
this an example of convergent or divergent
evolution?
Patterns in Evolution
Ch. 11.6, pp. 347-351
• Coevolution:
•
Species react to each other in many different
ways
•
Beneficial e.g. ____________________________
•
Parasitic e.g. _____________________________
•
Arms race e.g. ____________________________
Patterns in Evolution
Ch. 11.6, pp. 347-351
• Extinction:
•
•
Elimination of a species from Earth
• Unable to adapt to changing environments
Background extinction :
• Continuous over time
• Affects one to small number of species in an area
• Mass Extinction:
• Rare
• Global level
• Many species
• Five mass extinctions in last 600 million years
Patterns in Evolution
Ch. 11.6, pp. 347-351
• Patterns in evolution:
•
Punctuated equilibrium
•
•
Episodes of speciation followed by long periods of
little evolutionary change
Adaptive radiation
•
Diversification of one ancestral species into many
descendant species
• Different environmental pressures