Transcript Looking at the “natural” population below

Long
neck
Looking at the
“natural”
Looking at the “natural”
population
population below:
below:
Long
neck
Short neck
Which will
eat?
Looking at the
“natural”
Which
will
population below:
live?
Long
neck
Long
neck
Which will
have kids?
Short neck
1. Will the population be exactly the same
the next year?
no
2. What determines neck length?
DNA
3. Can the individual giraffes change their
DNA if they want to/try? Explain
No, can’t change their DNA
4. What process is being demonstrated
here?
Natural Selection/ Survival of the Fittest
True/False
5. Giraffes got long necks by stretching for leaves.
6. An individual organism (a giraffe) can change if
it wants to.
7. Individuals adapt to their environment and pass
the adaptations on to their offspring.
8. Individuals evolve.
Populations
Natural Selection Can cause a population to change
1. Variation
L = long neck, l = short neck
(simplified- may be polygenic – multiple genes):
LL, Ll, ll
gene pool – all alleles (genes)
in the population
2. Struggle to Survive
LL, Ll, ll
3. Most fit survive and reproduce LL x Ll
offspring: LL or Ll
What Causes Evolution?
1. NATURAL SELECTION – organisms with the
best FIT to the environment survive and
reproduce.
2. GENETIC DRIFT - Change in the gene pool of a
small population due to
a. Bottleneck chance
b. Founder Effect
What Causes Evolution?
1. NATURAL SELECTION – organisms with the
best FIT to the environment survive and
reproduce.
2. GENETIC DRIFT - Change in the gene pool of a
small population due to
chance
Bottleneck
Founder Effect
2. GENETIC DRIFT - Change in the gene pool of a
small population due to chance.
Gene pool – all the genes in a population at any one time. Each
person has two alleles for each trait.
a. Genetic Bottleneck
• Occurs when
species numbers
are low
• Results in little
genetic variety
• Everyone has very
similar genes in
population
2. GENETIC DRIFT - Change in the gene pool of a
small population due to chance.
a. Genetic Bottleneck - something (disaster) reduces
population size, killing randomly (unselectively).
Survivors genetic make up unlike original
population.
Elephant seal pop. 1890 = 20 (due to extensive
hunting), now = 30,000.
Problem: very little genetic variation.
Genetic bottlenecks are often
caused by human activities
• At the low point in their
population, California
sea otters . have
numbered a few dozen.
• Since 1972, after their
Marine Mammal
Protection, how much
genetic variation could
have occurred?
The Story of Cheetahs
Approximately 10,000 years ago, at the end of a time
called the Pleistocene Epoch also known as the Great
Ice Age (a geographical time period from
approximately 2 million to 10,000 years ago), the
world's environment underwent drastic changes in
climate.
Over a few thousand years,
75 percent of the mammal
species in North America, and
Europe died.When mammals
began to die, so did all the
cheetahs in North America
and Europe and most of those
in Asia and Africa.
Figure 13.22
The Story of Cheetahs (continued)
Cheetahs may have
migrated to more suitable
environment as ice
covered a large part of
the northern hemisphere
and sea levels fell.
The cheetah survived the mass extinction of
the Pleistocene Epoch, but its numbers were
greatly reduced. Brothers were left to
reproduce with sisters and parents with
siblings, which led to the founding of the
next generation, and inbreeding took place.
This occurrence - a severe reduction in population
- is called a "bottleneck." Every cheetah alive
today appears to be so inbred that genetically
they are as closely related as twins (two
offspring, or individuals born at the same birth).
What Causes Evolution?
1. NATURAL SELECTION – organisms with the best
FIT to the environment survive and reproduce.
2. GENETIC DRIFT a. Bottleneck
b. Founder Effect - few individuals colonize
isolated area, island/ lake. Genetic make up unlike
original population. Have limited genetic diversity.
Accounts for high frequency of inherited disorders in
populations.
What Causes Evolution?
1. NATURAL SELECTION
2. GENETIC DRIFT a. Bottleneck
b. Founder Effect
3. MUTATIONS – Changes in an organism’s DNA.
Very rare. Original source of genetic variation.
Raw material for natural selection.
4. MIGRATION
Patterns of
Evolution
Continental Drift
Geographic history of
Earth helps explain the
current distribution of
species.
Shifting continents = mass
extinctions (Pangaea),
climate change, habitat
destruction, change in
ocean currents, adaptive
radiations, isolation,
volcanoes, earthquakes etc
Currently North America
and Europe are drifting
apart by 2 cm per year.
Divergent Evolution
Organisms become
Species A
so different they
can no longer
interbreed and
Ancestral
Species
become a new
species
New Species share
common ancestor
Species B
Evolution & Speciation
Species B
Species A
Species A is separated into 2
isolated populations, each
affected by different
environmental conditions
Species C
Divergent evolution is the
basis of new species creation
• It requires
reproductive
isolation or
geographic isolation
of the new group
from the old.
• New traits forms
based on the
demands of the new
environment
Adaptive Radiation
• When several species evolve from an
ancestor each to fill a different niche of
the environment
HoneyCreepers - Hawaii
Convergent Evolution
Convergent Evolution
• When groups that
are NOT closely
related both change
in the same
direction due to
similar
environmental
pressures
• Species A
Similar Structures
Species B
Convergent evolution of unrelated
species in similar environments
• Cactus is a New World plant
(Americas)
• Euphorbia is an old world
(African) plant
• Both adapted to desert
conditions of heat and dry
climates
• What traits do both plants
share in common?
15. Analyzing Graphs The following graph shows drug
resistance that develops over time in the virus that causes
AIDS. Use the graph to answer the questions below.
a. What trend appears in all the patients by the end of
the third week?
b. Explain what happened to the virus population over
the ten weeks of exposure to the drug.
c. How do these data reflect a problem in treating
patients with the virus?