Evolution Review Power Point
• The purpose of this presentation is to
provide a basic overview of the concepts of
evolution.
• The topics for review were taken directly
from the Biology Keystone Assessment
Anchors and Eligible content. Content for this
lesson was derived from online sources and the Pearson,
Prentice Hall Biology: Exploring Life book (pages listed
correspond to this book)
• You are NOT required to review this
presentation we just felt it would be helpful for
those who were not taught this information or
who need a review.
Evolution
Mechanisms and Evidence
Chapters 14.2, 14.4, 15.1, 15.2, 15.3
Pages 299-304, 314-315, 310-316,
& 324-340
Objectives
• Explain how natural selection can impact allele frequencies
of a population
• Describe the factors that can contribute to the
development of new species (e.g., isolating mechanisms,
genetic drift, founder effect, migration).
• Explain how genetic mutations may result in genotypic and
phenotypic variations within a population.
• Interpret evidence supporting the theory of evolution (i.e.,
fossil, anatomical, physiological, embryological,
biochemical, and universal genetic code).
• Distinguish between the scientific terms: hypothesis,
inference, law, theory, principle, fact, and observation.
Populations and Gene Pools
• A biological population is a local group of
individuals belonging to the same
species
• Smallest level at which evolution can
occur
Individuals and Evolution
• Natural selection acts on individuals
AND affects reproductive success
• Natural selection ONLY becomes clear
when an entire population is tracked
over time
Evolutions of Populations
• Gene pool - all of the alleles in all the
individuals that make up a population
• Reservoir from which the next
generation draws its genes…..where
genetic variation (raw material of
evolution) is stored.
Changes in Gene Pools
• Mutations & sexual recombination lead
to genetic variation….& are RANDOM
• Natural selection (evolution) is NOT
random
• Environment favors genetic
combinations that increase survival and
reproductive success
Changes in Gene Pools
• Some alleles may become more common
in the gene pool
• Change in frequency of alleles –
• Usually expressed as decimal or
percentage
Changes in Gene Pools
• Be the bird eat the bug – Activity
shows how allele frequencies change
overtime
• http://www.nhm.ac.uk/natureonline/evolution/what-isevolution/natural-selection-game/theevolution-experience.html
Changes in Gene Pools
• Microevolution – evolution on the
smallest scale – a generation-togeneration change in the frequencies of
alleles within a population.
• Evolution based on genetic changes
Changes in Gene Pools
• Populations that do not undergo change
to their gene pools are not presently
evolving….. Hardy-Weinberg equilibrium
• Frequency of alleles in that gene pool
are constant over time.
• Natural populations don’t stay in this
for long
Genetic Drift
• Genetic drift – change in the gene pool of
a population due to chance.
• All populations subject to some
• Smaller populations are impacted more by
genetic drift….in smaller populations allele
frequencies can vary from one generation
to the next
Genetic Drift Bottleneck Effect
• Genetic variation in a population
decreases significantly due to a drastic
reduction of population size (and gene
pool).
Genetic Drift Bottleneck Effect
• May be due to disasters
(earthquakes, floods, droughts, and
fires)
• Could reduce the ability of
population to adapt to environmental
change
Genetic Drift
Founder Effect
• Change relates to genetic makeup of the founders
of the colony
• A few individuals colonize a new habitat (isolated
island, lake, etc.)
• Smaller colony, less genetic makeup diversity than
that of the larger population
• Chance reduces genetic variation
• Finches of Galapagos Islands
Gene flow
• Gene flow –exchange of genes between populations
• Occurs when fertile individuals (or gametes)
migrate between populations
• Reduces genetic differences between populations.
• Can mix neighboring pops into a single pop
w/common gene pool
Mutation
p.314
• Natural selection, genetic drift, or both
can influence whether the frequency of
a new mutation increases in a population
• If mutation is beneficial allele increases
• If mutation is harmful allele decreases
Mutation
• Key role in evolution as the original source
of genetic variation that is the raw
material for natural selection.
• Esp important as a source of variation in
asexually reproducing organisms (bacteria)
• In sexually reproducing organisms variation
is mostly due to scrambling of existing
alleles
Genetic drift, gene flow, and
mutation can cause
microevolution (changes in
allele frequencies)
Do NOT necessarily lead to
adaptation
Natural Selection and Fitness
p.314-315
• Natural selection = blend of chance and
sorting
• Chance… from mutation and sexual
recombination of alleles -> genetic
variation…RANDOM
• Sorting … accomplished by differences
in reproductive success… NOT random
Natural Selection and Fitness
• Fitness – contribution that an individual
makes to the gene pool of the next
generation compared to the
contributions of other individuals.
• Individuals whom are more fit/healthy
or well adapted to their environment are
more likely to survive to pass on genes
to offspring.
Speciation
15.1 p. 324-330
• Speciation – formation of new species
Development of New Species
4 factors that lead to Speciation
1. Behavioral/Reproductive Isolation
2. Geographic Isolation
3. Migration
4. Genetic Drift
Founder effect
Behavioral Reproductive Isolation
p. 325-326
• Timing – different breeding seasons
• Behavior - Two populations are capable
of interbreeding, but they have
different behaviors that prevent them
from breeding.
Behavioral Reproductive Isolation
p. 325-326
• Habitat – species adapted to different
habitats in the same general area. Ex.
one fish adapted to living along lake
edge others to open water.
• Others – reproductive structures
incompatible, reproductive facilitators
(insects) may only frequent one species,
zygote may fail to develop.
Geographic Isolation
p. 327-328
•
Form of reproductive isolation in which two populations are separated
physically.
Steps:
• 1. Start with an interbreeding population of one species.
•
2. The population becomes divided by a physical barrier. This can happen
when some of the population migrates or is dispersed, or when the
geography changes catastrophically (e.g., earthquakes, volcanoes, floods) or
gradually (erosion, continental drift).
•
3. The two populations can over time change relative to each other, because
each population has slightly different gene pools (random), different
environments with different food sources, shelter, predators, and each
gene pool undergoes its own mutation and natural selection.
•
4. Even if the barrier is removed and the two populations meet again, they
are now so different that they can no longer breed. They are
reproductively isolated and are two distinct species.
Geographic Isolation
p. 327-328
Examples:
A pond dries up to make two ponds.
A river is re-routed through a field.
A new road goes up.
A few seeds stuck on a bird’s feather
fall on a new island.
• A flood washes a few lizards or insects
to an island.
•
•
•
•
•
Geographic Isolation
Development of New Species
4 factors that lead to Speciation
3.Migration: Movement of animals from one place to
another. Changes the gene pool of a population
when animals with different genes enter or leave.
4.Genetic Drift: Random change in allele frequencies
that occurs in small populations.
• Founder effect: Extreme example of genetic drift.
Change in allele frequencies as a result of the
migration of a small group in a population.
• If a population begins with a few individuals—and
one or more carry a particular allele—that allele
may come to be represented in many of the
descendants.
Rate of Speciation
• Punctuated Speciation – evolutionary model
suggesting species often diverge in spurts
of relatively rapid change, followed by long
periods of little change.
• *NOTE: relatively rapid change here is
referring to GEOLOGIC time. So these
changes still take a very long time to occur
if we were to measure this compared to a
human life span.
INTERPRET EVIDENCE
SUPPORTING THE THEORY OF
EVOLUTION (I.E., FOSSIL,
ANATOMICAL, PHYSIOLOGICAL,
EMBRYOLOGICAL, BIOCHEMICAL, AND
UNIVERSAL GENETIC CODE).
Fossil
14.2 p 299-300
15.3
• Fossils typically form in sedimentary
rock
• Oldest layers tend to be at the bottom
of a series of bands of rock and
therefore oldest organisms are typically
found in the deepest (bottom) layers.
Fossil
14.2 p 299-300
15.3
• Fossil evidence shows that ancient
whales evolved from ancestors with hind
limbs.
• Whales today have the remains of what
appear to be hipbones but do not have
hind limbs.
Fossil
14.2 p 299-300
15.3
• Fossils provide scientists with
information about ancient animal’s
structures, behaviors, feeding patterns,
etc.
• Within the fossil record scientists have
found evidence of organisms changing
over time.
Anatomical and Physiological
14.2 p. 301
• Homologous structures – similar structure
found in more than one species that share
a common ancestor
• The front limbs of primates, cats, whales,
and bats all have similar arrangements of
bones even though they each use these
front limbs in different ways.
Anatomical and Physiological
14.2 p. 301
• Vestigial structures – remnant of a
structure that may have had an
important function in a species’
ancestors, but has no clear function in
the modern species.
• Ex. Whales today have small vestigial
hipbones but lack hind legs
Embryological
14.2 p. 302
15.2 p. 333
• Embryos of closely related organisms
often have similar stages in
development
Biochemical and Universal Genetic
Code
14.2 p. 303
• Siblings have similar DNA and protein
sequences
• Sequences of unrelated individuals of the same
species show more differences
• Likewise, species with similar DNA and protein
sequences probably had a common ancestor
• The greater the number of differences the
less likely they are to share a close common
ancestor
Distinguish between the
scientific terms
• Hypothesis – suggested, testable
answer to a well-defined scientific
question
• Inference – logical conclusion based on
observations
Distinguish between the
scientific terms
• Law – governs a single action or
situation, generalizes observations made
about that action or situation
• Theory – explanation of an entire group
of phenomena (much more broad,
complex, and dynamic); explains many
related observations and is well
supported by scientific evidence
Distinguish between the
scientific terms
• Law – a descriptive statement or equation that
reliably predicts events under certain
conditions
• Theory – well-tested explanation that makes
sense of a great variety of scientific
observations
• Principle – “a rule or law concerning a natural
phenomenon or the function of a complex
system; ‘the principle of the conservation of
mass”’ http://dictionary.kids.net.au/word/principle
Distinguish between the
scientific terms
• Fact – a reality or truth
• Observation – use of the senses to
gather and record information about
structures or processes in nature