Download File

4/2/2017
15-1 The Puzzle of Life’s Diversity
Evolution, or change over
time, is the process by
which modern organisms
have descended from
ancient organisms.
= Change over time
= Change in the frequency of
an allele in a population
Evolution is not
something that only
happened in the past;
it is still going on.
It does not happen to
individuals, it happens
to populations.
Charles Darwin
The Galapagos
Islands greatly
influenced
Darwin’s ideas.
Observed:
• Marine fossils atop mountains
• Organisms have variations based upon
environment
• Similarities between extinct fossils &
modern life
• Organisms seem remarkably well suited
for their environment
Darwin found 13 species of finches on
Galapagos Island. Each group of finches had
its own niche (an organism’s habitat and its
role in that habitat).
15-2 Ideas That Shaped Darwin’s Thinking
Most people in Darwin’s day believed that Earth was
only a few thousand years old, and that all of today’s
species had existed unchanged since their creation.
The shape of a tortoise’s shell corresponded
to its habitat.
• Tortoises on hot, dry islands had long necks and shells that curved
open around the neck and legs.
• On islands with rich vegetation, tortoise’s had a shorter neck and
dome-shaped shell.
1
4/2/2017
•Acquired Inheritance: Early theory where organisms could
acquire and pass traits after birth
•Cause: environmental changes forced individuals to change
- organisms strive to improve themselves
- unused body structures wasted away and most used
structures develop
•Early Belief: Giraffes & Long Necks
–Long necks are result of stretching to reach leaves
–Extra length was passed on to offspring
•Problem: Traits acquired after fertilization cannot be passed to
offspring
15.3 Darwin Presents His Case
The Theory of
Natural Selection
• Darwin mulled over his ideas
for 25 years before
publishing
• Alfred Wallace sent Darwin
an essay containing similar
ideas; they presented their
ideas together
• Darwin published his book 18
months later (1859)
Natural Variation
• Defined: Inherited traits that make an individual different
from others
• Natural variation is found in all types of organisms.
• Much of this variation can be inherited
Artificial
Selection
• Defined: Humans select (not naturally) traits thought to be
advantageous
• Humans created diversity choosing specific traits to breed
–Dogs, Crops, Livestock
• Only inheritable traits can be passed down
• Importance: Shows life can change over a period of time
2
4/2/2017
Dog traits have been
selected by breeders for
centuries to produce
various breeds.
Plants have been
bred to produce
certain traits for
human use also!
The Myth
These kittens have
variations
What is the beaver comic showing?
• Individuals don’t grow something
because they need it.
• Individuals don’t evolve.
Populations evolve!!!
Not all these
wildebeest will
survive
•Four factors:
1) Overpopulation: more offspring are born than can
survive
2) Variation: individuals of a population have differences
3) Adaptation: Some variations allow a better chance of
survival
4) Descent w/ modification: Over time, those with
advantages makeup more of the population
Struggle for Survival
•High birth rates and limited resources cause
competition
•Fitness: measure of the ability to survive & produce
more offspring; fitness is a result of adaptation
•Adaptations can be physical, behavioral, or
temporal
The Truth
- Natural selection
can act only on traits
that currently exist.
Adaptation
Defined:
An inherited trait that increases a population’s chances of
survival and reproduction in a particular environment
3
4/2/2017
Adaptations
Structural Adaptations
Mimicry
Behavioral Adaptation
Temporal Adaptation
Some cicadas reproduce every 13 years
while others reproduce every 17 years, so
the two groups never cross paths and
reproduce.
Blue-footed boobies have a courtship display
that is unique to their species; they will not mate
until that courtship display is completed.
Which rabbit is best adapted?
What happens when environments change?
Year 1 Background
Do the dark rabbits turn white? No! They get
eaten.
Year 10 Background
Those best adapted survive and reproduce.
4
4/2/2017
Changing Environments
•As environments change…
–Those with adaptation:
more likely to survive &
reproduce
–Those without adaptation:
more likely to perish
Limited
Resources
Overproduction
Variation
Populations produce too
many young; many must die
Individuals show variation; some
variations are more favorable
than others
•Populations do not grow
unchecked
Natural Selection
Natural selection favors
the best suited at the time
–Limiting Factors: food,
water, shelter, disease,
predators
Inheritance
Variations are
inherited. The best
suited variants leave
more offspring.
Summary of Darwin’s Theory of Evolution by Natural Selection
Over time, natural selection results in changes in inherited
characteristics of a population.
• Darwin’s principle states that over time, living species have
descended, with changes, from other species.
• This implies that all living organisms are related to one
another.
•Defined: Collection of every known fossil
•Most fossils found in sedimentary rock
•Age determined by depth
–new rock forms on top of older rock
•Evidence Conclusions:
1) Newer fossils are
more complex
2) Common ancestors:
relationships between
ancient & modern life
Fish
evidence
Reptile
Evidence
Whale
Evidence
Scales
Teeth
Long spine
Amphibian
Land
Evidence
evidence
Bird Evidence
Eyes on
Wolf-like
top of head
teeth
Wishbone
Bony
Fins
Foundtail
in dried up
oceans
Found in driedup oceans
Wrist bones
Hind
legs
Feathers
• AKA: Transition Fossils
–Archaeopteryx: shares both bird & reptile features
–Basilosaurus: shares whale & land mammal features
–Tiktaalik: shares fish & amphibian features
• Evidence Conclusion : Indicates common ancestry
5
4/2/2017
•Different
species show
similar
development
patterns
•Different body
plans become
noticeable
later in
development
•Evidence
Conclusion :
Indicates
common
ancestry
• Defined: similar body structures with very different
functions
• Different environments lead to adaptations
– Ex: The forelimbs of animals
• Evidence Conclusion : Indicates common ancestry
•Defined: Organs which have lost
most or all their original function
•Vestigial Human Parts:
• Defined: similar function with very different
structures
• Analogous structures are not evidence of a common
ancestor.
–Gill slits = once used to breath
oxygen in water
–Yolk sac = once used to nourish
developing embryo
–Tailbone = once used for balance
–Appendix = once used to digest
plants
–Wisdom teeth = once used to
grind plant tissue
•Evidence Conclusion : Indicates
common ancestry
Human Embryo w/ Vestigial Structures
Pythons have tiny femurs (leg bone)
6
4/2/2017
• DNA, RNA,
proteins
compared
• Genetic code
same for most
life
Ch. 16 Evolution of Populations
•More related species
have more similar
biochemistry
•Evidence
Conclusion:
Indicates common
ancestry
16.1 Genes & Variation
•Gene Pool: All alleles within a population
•Relative Frequency: number of times that an allele occurs
in a gene pool; usually expressed as a percent
How Twitter is upgrading our gene pool…
Allele Frequencies: Sum = 100%
Frequency of black allele = 12/20 = 60%
Frequency of white allele = 8/20 = 40%
Does gene frequency
equal
phenotype frequency?
Why or why not?
White allele is recessive to black allele.
No, because some black
mice carry the
recessive allele.
Sources of Genetic Variation
• Genetic variation can increase
chances some survive changing
environments
• Two main causes of genetic
variation:
1. Mutations: Random
changes to DNA sequence
affect phenotypes; may
affect fitness (ability to
survive and reproduce)
2. Gene Shuffling: During
meiosis, genes recombine
in varying patterns; does
NOT change the relative
frequencies of alleles!
7
4/2/2017
16.2 Evolution as Genetic Change
Natural Selection acts on
phenotypes, not genotypes
• Happens over generations
• Can lead to changes in allele frequency (Evolution!)
Freq. of green allele:
Individuals that are better suited to their environment
(have high levels of fitness) survive & reproduce most
successfully.
Types of Selection
Freq. of brown allele:
Types of Selection
Directional Selection—
Individuals at one end of
the curve have a higher
fitness than the rest.
Disruptive Selection—
Individuals at the upper and
lower ends of the curve have a
higher fitness; Selection
creates two distinct
phenotypes.
Types of Selection
Stabilizing Selection—
Individuals near the center of
the curve have higher fitness.
Genetic Drift
• Defined: Changes in allele frequencies due to chance
–NOT natural selection
• Bottleneck effect
–Results in a loss of genetic variation (alleles)
–More likely in smaller populations
–Example: Natural disaster
•Pre-forest fire: Green is best adapted (blend better)
•Post-forest fire: Brown more likely to reproduce
–Survival UNRELATED to adaptations
8
4/2/2017
Genetic Drift: Founder Effect
• Situation in which allele frequencies change as a
result of the migration of a small subgroup of a
population.
• Example: Hawaiian fruit flies descended from 1 main
type—very different from mainland fruit flies
Speciation
Defined: evolution of new species from an existing
species
• 5 factors that lead to evolution
Natural Selection
Gene flow
Mutations
Sexual selection
Genetic drift
Reproductive Isolation
• When populations are isolated for
a long time…gene flow stops
• When populations can no longer
mate or no longer reproduce fertile
offspring
• Final step in the development of a
new species
1) Geographic Isolation:
o Organisms isolated by
geographic barrier
Random DNA
mutations
Random DNA
mutations
Different
predators
Different
predators
Different
resources
Different
resources
16-3 The Process of Speciation
Species
•Defined: group of organisms that
can interbreed and produce fertile
offspring
–Different species rarely breed
–Interspecies breeding often
results in sterile offspring
•Ex: Horse x Donkey = Mule
•Ex: Lion x Tiger = Liger
–New species = when unable to
successfully reproduce
Gene Flow (Migration)
•Defined: Movement of alleles from one
population to another
- Increases variations in a
population
- Keeps differing populations similar
•If gene flow is prevented
- No variations (alleles) exchanged
- Populations are isolated
- Organisms adapt to their own
environment
- Can lead to speciation!
9
4/2/2017
Reproductive Isolation
Reproductive Isolation
• When populations are isolated for a
long time…gene flow stops
• When populations can no longer mate
or no longer reproduce fertile offspring
• Final step in the development of a new
species
1) Geographic Isolation:
o Organisms isolated by geographic
barrier
2) Behavioral Isolation
o Organisms isolated by differing
mating rituals
Current Evolution:
If the mating calls do not attract
each other, will they reproduce?
Is gene flow stopped?
• When populations are isolated for a
long time…gene flow stops
• When populations can no longer mate
or no longer reproduce fertile offspring
• Final step in the development of a new
species
1) Geographic Isolation:
If one group mates during the spring…
o Organisms isolated by geographic
Is gene flow stopped?
barrier
And the other mates during the fall…
2) Behavioral Isolation
o Organisms isolated by differing
mating rituals
3) Temporal Isolation
o Organisms isolated by differing
times of reproduction
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
When
The antibiotics
infected with
are absorbed
a bacteria,into
we the
take
antibiotics.
bacteria.
–Ex: Antibiotics
eliminating unfit bacteria
Bacteria A is more likely to survive and _________________.
REPRODUCE
antibiotic
antibiotic
Alexander
Fleming
discovered the
first
antibiotic…
penicillin
antibiotic
antibiotic
Bacteria A
Bacteria B
antibiotic
antibiotic
Bacteria A
antibiotic
Bacteria A has genes to create
enzymes that destroy the antibiotic
antibiotic
Bacteria B does not have the genes to
make the enzymes to destroy the antibiotic
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
–Ex: Pesticides
eliminating unfit pests
10
4/2/2017
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
–Ex: Pesticides
eliminating unfit pests
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
Some “pests” are able to resist the
pesticides and survive. They will
reproduce with others who are
resistant. Over time, the entire
population is resistant.
–Ex: Antibiotics
eliminating unfit bacteria
–Ex: Pesticides
eliminating unfit pests
Pesticides pesticides pesticides pesticides pesticides pesticides
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics eliminating
unfit bacteria
–Ex: Pesticides eliminating
unfit pests
–Ex: Antivirals…
–Ex: Fungicides…
•This is natural selection!
–Allows resistant to
survive and reproduce
Read before the video, answer after…..
1. Why is the Russian prison system considered to be
"ground zero" in the fight against TB?
2. What is responsible for the evolution of TB strains
that are resistant to multiple drugs?
3. How does the misuse of antibiotics affect the
evolution of disease-causing bacteria? Use the
theory of natural selection to explain the growing
resistance to antibiotics.
4. Why should we care about a resistant strain of TB
in Russia?
Why Does Evolution Matter Now?
11