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Notes and warm ups
Cell Phones
Evidence for Evolution
• Lets first make sure we are on the same page
– Organisms do NOT evolve….populations do
– Evolution does NOT explain where life came from,
just why populations change
– The mechanism of evolution is Natural Selection
(so when I say either term….I mean the same
Lamarck’s BAD IDEA
Lamarck’s BAD IDEA
• Cut the tail off of a
female and a male
• Breed the mice
• What are the chances
that the offspring will
not have tails?
Two kinds of Evolution
• Change above a species
• New characteristics such as
• Most of the events on our
timeline represent
• Change at the species level
• Change in a population
from generation to
• Give some examples of
Natural Selection
• Is a process and can be divided into five steps
– Genetic variation--all populations have genetic diversity
that gives them individual combinations of traits
– Overpopulation—all populations compete for limited
resources due to over reproduction
– Environmental change—all environments are dynamic
– Differential Reproduction (Survival of the “fittest”)—when
environments change, the best adapted members of the
population survive and reproduce
– Population change—the genes of the reproducing
organisms (and thus the traits) increase in the population
Natural Selection
• Adaptations do not happen in response to
• Adaptations are already present in the
population and make the organisms MORE
SUCCESSFUL in the NEW environment
• For example: there are brown bears and
white bears….if there is another ice age which
will be best adapted?
Natural Selection Simulation
• Genetic variation-- we will model a variety of
different modes for nutrient acquisition
• Overpopulation—we will compete for limited
• Environmental change—all sources of nutrition
destroyed except for one
• Differential Reproduction—only those of you who
can collect AND eat 5 “nutrient nodules” survive
and reproduce (save the wrappers as evidence)
• Population change—those of you who survive get
to pass on your traits
Natural Selection CAN NOT produce
perfect organisms because….
• Selection can only edit existing variation
• Selection is limited by environmental
change…which is always changing
• Adaptations are often compromises– best
solution for the least energy
• Chance, selection and the environment
Increase Genetic Variation
Mutations (point and chromosome)
– Only passed on if they affect the gametes
– Only source of NEW alleles
– Most mutations are HARMFUL
Sexual reproduction
– Crossing over (20,000 genes in the human genome)
– Independent assortment (223 possible combinations)
– Random Fertilization (223 X 223 possible combinations)
– Conjugation
– Transformation
– Transduction
Gene Flow
– Immigration
– Emigration
– Migration
Decrease Genetic Variation
• Small populations
– Fixed genes
– Isolation (geographic or genetic)
• Differential reproduction
– Sexual selection (peacocks, rams)
– Self pollination/self fertilization
• Asexual reproduction
• Low mutation rate
• Gene Linkage Groups
Genetic Variation
• Why is genetic variation important?
• What would happen to a population if the
environment changes but they have NO
• Low genetic variation is usually caused by fixed
alleles– meaning that all organisms are
homozygous for that trait.
Speciation Jig Saw
Founder effect
Mechanical isolation
Bottleneck effect
Gametic isolation
Gene flow
Reduced hybrid viability
Prezygotic barriers
Reduced hybrid fertility
Postzygotic barriers
Hybrid breakdown
Habitat isolation
Polyploid speciation
Behavioral isolation
Adaptive radiation
Temporal isolation
Genetic drift