Download mechanisms for evolution - Fall River Public Schools

MECHANISMS FOR EVOLUTION
Honors Biology
REVIEW
• Evidence for Evolution
and Examples
• What is Natural Selection?
• How did Darwin develop
theory of
Natural Selection?
PATTERNS OF EVOLUTION
• Coevolution:
– 2 or more species evolve in association with one
another
– Predators and Prey
– Plants and Pollinators
– Bats and Flowers
PATTERNS OF EVOLUTION
• Convergent Evolution:
– Organisms that look similar
but are not related
– Analogous features
– Similar environments
– Sharks and Dolphins
PATTERNS OF EVOLUTION
• Divergent Evolution
– 2 or more related populations or species become
more and more dissimilar
– Usually a response to new habitat
– Can result in new species
– Adaptive radiation
– Artificial Breeding
– Humans and Chimps
POPULATION GENETICS AND
EVOLUTION
• What did Darwin know?
– Environment is important
– Competition for Resources
– Natural Selection: Individuals with traits more
suitable for a particular environment are more
likely to survive AND reproduce
• What did Darwin not know?
– Where does variation come from
POPULATION GENETICS
• We now know that variation comes from
genetics; no variation  extinction
• Population genetics: study of evolution from
genetic point of view
WHAT CAUSES VARIATION
• Need to think about variation in GENOTYPE
– Mutation: change in DNA/chromosomes
– Recombination: during meiosis
– Random fusion of gametes
OTHER MECHANISMS FOR EVOLUTION
• Things that upset genetic equilibrium
• Using Hardy Weinberg you can predict
genotypes; Only in hypothetical populations
MUTATION
•
•
•
•
•
Change in DNA or chromosomes
Make new alleles for a trait
Many are harmful
Can be neutral (code for same amino acid)
Some are beneficial
MIGRATION/GENE FLOW
•
•
•
•
•
Call it gene flow
Populations exchange genes
Increases within group variation
Decreases between group variation
DOESN’T HAVE TO BE MIGRATION
GENETIC DRIFT
• Occurs in small populations
• Allele frequencies shift as a result of RANDOM
events
• Coin Toss
• Founders Effect; Bottleneck
NONRANDOM MATING
• Sexual Selection
• Positive assortative mating – mate with
someone similar
• Negative assortative mating: redheads!
NATURAL SELECTION
• Darwin and neoDarwinians believe is the most
important way evolution occurs
• Types of Selection
STABILIZING SELECTION
• Average form are selected for
• Lizards:
– Predators caught slow small and large visible
– Select for medium size
DIRECTIONAL SELECTION
• Individuals with an extreme trait are selected
for
• Anteaters with long tongues
DISRUPTIVE SELECTION
• Individuals with either extreme are selected
for
• Limpet shell color; light and dark on different
surfaces
SEXUAL SELECTION
•
•
•
•
Choosing mates based on traits
Intersexual Selection
Intrasexual Selection
Bird Color
SPECIATION
• If enough changes accumulate  new species
• Biological concept of species: organisms can
mate and produce fertile offspring; not just
morphological (what they look like)
• Isolating mechanisms  speciation
– Geographic isolation
– Reproductive isolation
SPECIATION
• Rates of speciation
– Gradualism: species
evolve gradually over time
– Punctuated equilibrium:
species go through times
of fast change and slow
or no change