Transcript Presentation

11.1 KEY CONCEPT
A population shares a common gene pool.
 Genetic
variation leads to phenotypic variation.
 Phenotypic variation is necessary for natural selection.
 Genetic variation is stored in a population’s gene pool.
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made up of all alleles in a population
allele combinations form when organisms have offspring
 Allele
frequencies measure genetic variation.
– measures how common allele is in population
– can be calculated for each allele in gene pool
1. Calculate the allele frequency for G(Green frogs) in the population
2. Calculate the allele frequency for g (brown frogs) in the population
 Mutation
is a random change in the DNA of a gene.
– can form new allele
–How can mutations be
passed on to offspring?
• Recombination forms new combinations of alleles.
– usually occurs during meiosis, What is the process called?
– parents’ alleles
arranged in new
ways in gametes
 Hybridization
is the crossing of
two different species.
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occurs when individuals can’t find
mate of own species
Much more successful/common in
plants
topic of current scientific
research
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A normal distribution graphs as a bell-shaped curve.
– highest frequency near
mean value
– frequencies decrease
toward each extreme
value
• Why is this curve called
“normal”?
• Traits not undergoing
natural selection have a
normal distribution. Why?
 Microevolution
is
evolution within a
population.
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observable change in the
allele frequencies
can result from natural
selection
How does natural selection
cause a change in allele
frequencies?
 Natural
paths.
selection can take one of three
– Directional selection favors phenotypes at one
extreme.
– Bacteria, Greyhounds
 Natural
paths.
selection can take one of three
– Stabilizing selection favors the
intermediate phenotype.
– Gall flies, Siberian Huskies
– What happens to the allele frequency
in this distribution?
 Natural
selection can take one of
three paths.
– Disruptive selection favors both
extreme phenotypes.
– What happens if the middle cuts off
completely?
11.1 Genetic Variation Within Population
A
B
C
Match each graph with
the correct type of Natural
Selection:
1. Directional
2. Disruptive
3. Stabilizing
A
plant that is too short may not be able to
compete with other plants for sunlight.
However, extremely tall plants may be more
susceptible to wind damage.
 Throughout
the wet seasons, small seeds are
more common and there are such a large
supply of the small seeds that the finches
only eat small seeds. The smaller, smoother
beaks make picking up the small seeds easier
and become more common in the population.
 Early
breeders were interested in dogs with
the greatest speed. They carefully selected
from a group of hounds those who ran the
fastest. From their offspring, the greyhound
breeders again selected those dogs who ran
the fastest. By continuing this selection for
those dogs who ran faster than most of the
hound dog population, they gradually
produced a dog who could run up to 64km/h
(40mph).
 In
a species of African butterfly the
colorations range from a reddish yellow to
blue. In both cases, these extremes of
color, from different ends of the
spectrum, mimic other species of
butterflies that are not normally the prey
of the local predator group of birds and
other insects. Those butterflies that are
moderate in coloration are eaten in far
greater numbers that those at the
extremes of the color spectrum.
 Babies
of low weight lose heat more quickly
and get ill from infectious disease more
easily, whereas babies of large body weight
are more difficult to deliver through the
pelvis. Infants of a more medium weight
survive much more often. For the larger or
smaller babies, the baby mortality rate is
much higher.
 Suppose
there is a population of rabbits.
The color of the rabbits is determined by
incomplete dominance, with a black
coloring, white coloring, and gray
heterozygous coloring. If this population
of rabbits were put into an area that had
very dark black rocks as well as very
white colored stone, the rabbits with
black fur would be able to hide from
predators amongst the black rocks and
the white furred rabbits would be able to
hide in the white rocks, but the grey
furred rabbits would stand out in both of
the habitats and would suffer greater
predation.
 Think
of an example for each of the types of
distributions for natural selection
 Use
a deck of cards to represent a population of
island birds. The four suits represent different
alleles for tail shape. The allele frequencies in the
original population are 25% spade, 25% heart, 25%
club, and 25% diamond tail shapes.
 Turn to page 337 in the books. With your groups,
follow the procedure for the lab. Just do the
activity, don’t worry about the questions right now.
 Gene
flow occurs when
individuals join new
populations and reproduce.
 Gene flow keeps neighboring
populations similar.
 Low gene flow increases the
chance that two populations
will evolve into different
species.
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What is a species?
Why would low gene flow
create new species?
bald eagle migration
 Genetic
drift causes a loss of genetic diversity.
 It is most common in small populations. Why?
 A population bottleneck can lead to genetic drift.
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It occurs when an event
drastically reduces
population size.
Example?
The bottleneck effect is
genetic drift that occurs
after a bottleneck event.
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The founding of a small population can lead to genetic drift.
– It occurs when a few individuals start a new population.
– Can you think of an example of when this might occur?
– The founder effect is genetic drift that occurs after start
of new population.
 Genetic
drift has negative effects on a population.
– less likely to have some individuals that can adapt
– Why does that occur more in small population?
– Penny Activity:
Flip the penny 3 times, record how many head and
how many tails you flipped.
Flip the penny 7 more times, record how many heads
and tails you flipped.
Which results were closer to the 1:1 ratio you expect
to get?
– harmful alleles can become more common due to
chance
 Sexual
selection occurs
due to higher cost of
reproduction for
females.
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males produce many
sperm continuously
females are more limited
in potential offspring each
cycle
Result: Females are
picky!
 There
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are two types of sexual selection.
intrasexual selection: competition among males
– Example:
intersexual selection: males display certain traits to
females
– Example:
These birds have
huge red air sacs
which make them
easier for
predators to spot.
Why would they
have evolved
these, then?
Male Irish elks,
now extinct, had
12-foot antlers.
Describe how
sexual selection
could have caused
such an
exaggerated trait
to evolve.
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Populations become isolated when there is no gene flow.
 Isolated populations adapt to their own environments.
 Genetic differences can add up over generations.
Two small, isolated
populations of dolphins in Tin
Can Bay and the Great Sandy
Strait are at risk of extinction,
and are the focus of a study by
Southern Cross University
researcher Daniele Cagnazzi.
Mr Cagnazzi has been
studying dolphins along the
Queensland coast for the last
three years.
~ABC News
 Reproductive
isolation can occur between isolated
populations.
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members of different populations cannot mate successfully
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Prezygotic: temporal isolation, behavioral isolation
Postzygotic: hybrid sterility
final step to becoming separate species
 Speciation
is the rise of two or more species from one
existing species.
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Behavioral barriers can cause isolation.
 called behavioral isolation
 includes differences in courtship or mating behaviors
 Geographic
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called geographic isolation
physical barriers divide population
 Temporal
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barriers can cause isolation.
barriers can cause isolation.
called temporal isolation
timing of reproductive periods prevents mating
 Natural
selection can have direction.
 The effects of natural selection add up over time.
What examples can you think of
of convergent evolution?
Wings of insects
and birds; fins/tails
of sharks and fish
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Divergent evolution describes evolution toward different traits in
closely related species.
red fox
kit fox
ancestor
Other examples of divergent
evolution?
 Two
or more species can evolve together through
coevolution.
 evolutionary paths become connected
 species evolve in response to changes in each
other
 Coevolution
can occur in beneficial relationships.
THINK!
Why do the stinging ants live
in the holes of the thorns that
are supposed to protect the
plant from herbivores that
would eat the leaves?
How does the plant benefit?
How does the ant benefit?
 Coevolution
can occur in competitive
relationships, sometimes called evolutionary.
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Extinction is the elimination of a species
from Earth.
Background extinctions occur continuously
at a very low rate.
 Same rate as speciation
 Few species in small area
 caused by local changes in environment
 Mass
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extinctions are rare but much more intense.
destroy many species at global level
catastrophic events
5 in last 600 million years
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A pattern of punctuated equilibrium exists in the fossil record.
 theory proposed by Eldredge and Gould in 1972
 Episodes of speciation occur suddenly followed by periods of
little change
 revised Darwin’s idea
 Many
species evolve from one species during adaptive
radiation.
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ancestral species diversifies into many descendent species
descendent species
adapt to different environments