More Natural Selection Info
• Describe Natural Selection including the 3
things needed for it to occur
• Define adaptation
• List and describe five examples of natural
and artificial selection
Natural Selection
• 1. There is competition for limited resources
• 2. There is natural variation (behavior, traits)
• 3. The variation is inherited
• The outcome of variation in heritable traits
that affect survival and reproduction
Adaptation
• The consequence of natural selection is
adaptation
• Adaptation: some heritable aspect of form,
function, behavior or development that
improves the odds for surviving or
reproducing in a given environment.
Artificial Selection
http://www.gly.uga.edu/railsback/1122/1122Dogs.jpeg
Artificial Selection
http://www.bio.miami.edu/dana/160/artificialselection.jpg
Natural Selection
http://www.museums.org.za/bio/insects/cockroaches/
http://home-supplies.best-emporium.com/cat-125/Cleaning-Sanitation/Cleaning-Chemicals/Rodenticide-Insecticides
Natural Selection
Staphylococcus aureus: antibiotic resistance
Population Information
• Define population
• Describe the basis and source of heritable
variation within a population
• If there are heritable variations within a
population, when does evolution not occur?
How would you define
POPULATION?
• all organisms that constitute a specific
group (species) in a specific
habitat/environment
Review of Genetics
•
•
•
•
•
•
Cells are the basic unit of life
Cells have DNA
DNA contains genes
Genes code for proteins, usually enzymes
Genes that differ slightly are called alleles
Different alleles make different forms of the same
enzyme
• These enzymes determine an organisms phenotype
• Alleles can be inherited
Population Genetics
• Gene pool: all the alleles of all the genes in all
the individuals in a population
• Each organism will have a unique combination
of alleles and, therefore, a unique phenotype
• Unique combination of alleles
–
–
–
–
–
Mutation
Crossing-over
Independent assortment
Fertilization
Change in chromosome number or structure
Population Genetics
• Allele frequency: relative
proportion of one allele for one
gene
• Evolution: change in the allele
frequency within a population
How does Evolution Occur?
• Describe how evolution can occur
–
–
–
–
–
Mutation
No gene flow
Small population size
Non-random mating
Natural selection
• Disruptive
• Directional
• Stabilizing
Violation of equilibrium: mutation
• Mutations are rare (1/100,000 gametes)
• Mutations can be:
– Helpful
• Depends on
environment
– Neutral
– Harmful
• Lethal mutation
Gene Flow
• Individuals, and their alleles, move
into and out of populations
• The physical flow counters the effects
of:
– mutation
– natural selection
– genetic drift
Small Population Size
• Hypothesis: how often will you get tails?
• Flip a coin ten times:
– # heads
– # tails
• Everyone flip a coin ten times:
– # heads
– # tails
• Discuss the difference between 10 and 200
events: sampling error
Small Population
• Random events can have drastic effects on
the allele frequencies in a small population:
Genetic Drift
• Two examples:
– Founder effect
– Bottleneck
phenotypes of original population
Founder
Effect
A seabird carries a few seeds, stuck
to its feathers, from the mainland to
a remote oceanic island.
phenotype of island population
Bottleneck Effect: Elephant seal
Reduction of a population’s gene pool
produced when a few members
survive the widespread elimination of
a species.
Año Nuevo
State Park
http://www.aad.gov.au/default.asp?casid=1239
Non-random mating
• Do humans mate randomly?
• How do people pick a mate?
Non-random mating: 3 types
• Assortive – shifts genotype frequency
– Organisms choose a mate with the same
genotype as themselves.
– Organisms choose a mate with a different
genotype from themselves.
• Self-fertilization – shifts genotype frequency
– Organism mates with itself
• Sexual selection –shifts allele frequency
– Some genotypes mate more successfully than
others
Assortive Mating
Self-fertilization
Sexual selection
http://subjunctive.net/photoblog/2003/peacock-wooing-peahen.jpg
Natural Selection
• Evolution due to natural selection results from
unequal reproduction of various alleles
• Natural selection acts on phenotypes but affects
genotypes
• Adaptations help an individual survive and
reproduce
Agents of Natural Selection
• Abiotic factors
– Climate
– Geology
– Other non-living factors
• Biotic factors
– Competition
• Food, Shelter, Mating
– Interspecies Interactions
• Predation
– Sexual Selection
Number of
individuals
Number of
individuals
Directional
Selection
Range of values at time 1
Range of values at time 2
Number of
individuals
3 Modes of
Natural
Selection:
Range of values at time 3
Number of
individuals
Number of
individuals
Stabilizing
Selection
Range of values at time 1
Range of values at time 2
Number of
individuals
3 Modes of
Natural
Selection:
Range of values at time 3
Number of
individuals
Number of
individuals
Disruptive
Selection
Range of values at time 1
Range of values at time 2
Number of
individuals
3 Modes of
Natural
Selection:
Range of values at time 3