Transcript Evolution Review S

Bio 7: General Biology II
Evolutionary, Organismal, &
Ecological Biology
Dr. Diane Livio
[email protected]
myetudes.org/portal
MW 2:30-4:30 (CMS 229)
TTh 3:30-4:30 (CMS 106)
About this course
• Majors course – rigorous and challenging,
designed to be rewarding
• Student responsibilities
• Review the syllabus
• Check Etudes regularly
Expectations & Goals
• What is expected of you?
• What do you expect of me? Or your class
mates? Of the course?
• First module on Etudes has help!
“Learn How You Learn”
www.vark-learn.com
Evolutionary Processes
"Nothing in biology makes sense except in the
light of evolution" - Theodosius Dobzhansky
Scientific Theory
• Def: a proposed
explanation for a
very general class
of phenomena,
supported by a
large body of
evidence
• Possesses both
pattern and
process
components
Theory of Evolution
• On the Origin of Species (1859)
• All life evolved gradually from one primitive
species [lived 3.5 bya]
– Split off into many diverse species over time
– Mainly by natural selection
Pattern of Evolution
• Descent with modification
– Inherited characteristics in
a population of a species
change over time
– Sometimes population
changes over time to form
a new species
– Newer species descend
from older species
Macroevolution
• Pattern of
evolution over
large scales
– Larger than the
species level
– Over geologic
time scale
How old is the Earth?
How old is life?
Earth’s Early History
• Estimates of Age of Earth/Solar System
-- Current estimate: 4.54 by
• Oceans formed by 3.8 bya
• No O2, much solar radiation
• Life – 3.6 to 3.8 bya
Oldest fossils: 3.5 by
Most history of “higher” organisms in
most recent 500 million years…
Macro- vs Micro-
Process of Evolution
Microevolution: the change in allele frequencies in
a population over time
Population:
a group of
individuals of one
species living in a
particular place
DNA
• Genetic info –
heritable
• Genes: code for
proteins to make
and maintain
organisms
• Allele: form of a
gene
GENOME
CHROMOSOMES
NUCLEOTIDES
GENOTYPE vs
PHENOTYPE
Process of Evolution
Microevolution: the change in allele frequencies in
a population over time
Mechanisms of Evolution:
1. Mutation
2. Genetic Drift
3. Gene Flow
4. Natural Selection
Mutation in DNA
• Def: change to the nucleotide bases (adds
variation to the population)
Mutation = Source of DNA Variation
DNA Replication =
Potential MISTAKES
Genetic Drift
• Def: any change in allele frequencies in a
population that is due to chance
– Random with respect to fitness
• More pronounced in small populations
• Drifting allele frequency could lead to loss of allele
or fixation (100% frequency)
Fig. 23.4
Genetic Drift - how it occurs:
• Genetic bottleneck – sudden reduction in # of
alleles in a population
Conservation biologists manage
“gene pool” of species with small
population sizes to prevent loss
of alleles through drift.
Genetic Drift - how it occurs:
• Founder’s effect – change occurs when a new
population is established
– Small subset does not represent allele frequencies of
source population
Gene Flow
• Def: change
in allele
frequency
due to
migration
between
populations
• Gene Flow: movement of alleles from one
population to another
– Tends to make one or both populations look more like
the other
Charles Darwin: The Origin of Species (1859)
• Identified natural selection
as the major mechanism of
adaptive evolution
• Much focus on survival
aspect of reproduction 
“survival of the fittest”
Adaptive Evolution
Adaptation = a heritable trait that increases an
individual’s ability to produce offspring (its
fitness) in a particular environment relative to
individuals lacking the trait
Natural Selection
• Process by which heritable variation leads to differential
success in survival and reproduction
• Differential reproductive success can result from
differences in survival, fecundity, and mating success.
• Artificial selection –
deliberate
manipulation by
humans
Summary
• Natural selection adapts a population to its
environment.
• Selection operates on individuals.
Evolution occurs in populations and
species.
• Other mechanisms of evolution: mutation,
drift, gene flow.
Speciation
• Species: “an evolutionarily
independent population or group of
populations”
– Reproductive compatibility
– Similar physical appearance
– Shared, unique genetic history
• Allopatric vs sympatric speciation
– Physically separated populations vs
“living together”