Transcript Chapter 17 Mechanisms of Evolution

Chapter 17.2 Genetic Change
17.3 Speciation
1
Definitions
 Gene pool: All alleles of the population’s
genes.
 Allelic frequency: % of a specific allele in
the gene pool. Example: See Figure 5 Page
404 Snapdragon Flower
 Genetic Equilibrium: This exists when the
frequency of alleles remains the same over
generations. The population is not evolving.
2
5 Different “Forces” That
Can Cause Evolution





1. Gene Flow
2. Non-random Mating (Sexual Selection)
3. Mutation
4. Genetic Drift
5. Natural Selection
3
Gene Flow
 Gene Flow occurs when genes are
added or removed from a population
 Example: Migration
 These caribou are migrating from one place to
another. If they meet other groups of caribou
4
and interbreed, gene flow may occur.
Non-random Mating
(Sexual Selection)
 Females sometimes select mates based
on the male’s size, color, ability to gather
food, or other characteristics.
 Example: The vibrant red stripe of the blue
muzzle of this male (right) mandrill baboon
does not appear in females (left).
5
Non-random Mating
(Sexual Selection)
6
Mutation
 When the DNA code of organisms
changes randomly (Creates new alleles)
7
Genetic Drift
 Chance events, such as fires, floods or storms,
can cause rare alleles to be lost.
 This occurs more often in populations that are
small in size. Genotypes
can change as a result.
 Example: A wildflower population ... consisted
 of only 25 plants. Assume that 16 of the plants
 have the genotype AA for flower color, 8 are Aa, and only 1
is aa. Now imagine that three of the plants are accidently
destroyed by a rock slide before they have a chance to
reproduce. By chance, all three plants lost from the
8
population could be AA individuals.
Natural Selection
 Can remove
individuals with
certain traits from a
population.
 The alleles for those
traits may become
less common in the
population over time.
 Example: Horse
Evolution
9
Evolutionary Fitness
 How long an individual can survive
and how many offspring they can
produce to pass genes to future
generations???
 This is their “Evolutionary
Fitness”.
10
Who has the Higher
Evolutionary Fitness?
11
3 Types of Natural Selection
 Directional Selection – favors one of the
extreme variations of a trait
 Stabilizing Selection – favors average
individuals
 Disruptive Selection – favors individuals
with both extremes of a trait (eliminates
intermediate phenotypes)
12
13
14
17.3 Biological Species
Concept
 When Males and Females of the same
species reproduce and their offspring are
fertile and can pass on their genes they
are considered a species.
15
Sterile Hybrids
Liger
Mule
16
Speciation
 Speciation occurs when members of
similar populations no longer interbreed
to produce fertile offspring within their
natural environment.
 Example: Squirrels that live in the Grand
Canyon
17
Species definition does
not always apply
 Some organisms reproduce Asexually:
Bacteria and Archaebacteria
18
Types of Speciation
 a. Geographic Barrier- A physical barrier
that prevents interbreeding (Mountain,
River, Island)
 b. Change in Mating Behavior and Timing
 c. Change in Niche (Food source)
19
a. Geographic Isolation
20
Geographic Isolation
Examples of how this can happen:
1. A pond dries up somewhat to make two
ponds,
2. A river becomes re-routed so that it cuts
through a field,
3. Two land masses drift apart over time,
4. A few seeds stuck on a bird's feather fall
by chance on a new island
5. A new road goes up between 2 fields,
6. A flood washes a small population of
lizards to an island....etc
21
Geographic Isolation
22
Change in
b. Mating Behavior and
Timing
 Many species that sexually reproduce
have specific behaviors for attracting
mates, such as a pattern of sounds or
actions.
 Example: The pickerel frog and the
leopard frog are closely related species.
Differences in mating times may have
23
caused their reproductive isolation.
Timing
 Similar species have different breeding
seasons
Eastern Spotted
Skunk
Western Spotted
Skunk
24
Bizarre Mating Rituals
 The male anglerfish latches onto the female
like a parasite, living off her food and fertilizing
her when she's ready to lay eggs.
 The male octopus's penis breaks off during
mating, but don't worry, it will grow back the
following season.
25
Bizarre Mating Rituals
 Emperor Penguins travel as far as 70 miles on
foot to reach the breeding site. They look for
their mates by making a bugling call. Once
they find one another, they stand breast to
breast, repeatedly bow to each other and sing.
26
c. Change in Niche
 Divergence can happen when
populations use different niches
 Example: The members of a particular
population of insects live and feed high up in
the trunks of trees. As time passes, some
members of the population begin to feed on
different parts of the trees. Eventually the 2
groups diverge and no longer interbreed.
27
Artificial Speciation
Diane Dodd’s fruit fly lab, 1989
28
What is Extinction?
 When a species fails to produce any offspring
 99% of all species that have ever lived on
Earth are now extinct
Wooly Mammoth
T Rex
Dodo Bird
Tasmanian Tiger
29
The End
30