Mechanisms of Evolution: Power Point and associated vocabulary

1. Allopatric speciation: The Grand Canyon is a
geographical barrier separating the Albert and Kaibab squirrels

2.  Population – a group of organisms that interbreed
 Each population shares a gene pool (the different alleles
present in the population)
 Each population has a relative frequency of each alleles, or
the number of times the allele occurs in the gene pool.
 The frequency of alleles in a population tend not to change
unless there is an outside force causing it

3.  Mutations are inheritable changes to the genotype
of an organism
 Mutations occur randomly and spontaneously within a
population
 Most mutations are harmful, but some are useful
 Mutations can affect allele frequency in a population by
1. Adding new alleles for a trait
2. Changing the amount of each allele present
 It can take a long time to eliminate a mutation and a
long time for a new mutation to become prevalent

4.  There are 5 mechanisms that can change the
allele frequencies in a population
1. Mutation
2. Migration
3. Genetic Drift
4. Non-random Mating
5. Natural Selection

5.  Movement into and out of a population can
change the allele frequency in a population’s
gene pool
 Immigration can ADD individuals with variations
to the population
 Emigration can REMOVE individuals with
variations from a population. Can you think of
large human immigrations and emigrations within
the last 150 years?
 Many species encourage migration which can
cause more gene flow which is the process of
transferring genes among different populations

6.  Genetic drift is the random changes in
allele frequency due to population size.
 In
smaller populations the allele frequency
can change more rapidly than in larger
populations

7.  The founder effect
occurs when a few
individuals from a larger
population colonize a
new area.
• Ex. Amish community.
 The allele frequency
of this population may
differ from the larger
population because of the
limited number of individuals

8.  Havinga limited number of individuals can
also impact mating.
 Non random mating can influence allele
frequencies because:
• Mates can be limited by geography
• Mates can be chosen for their traits
• Mates can be more closely related to one another

9.  Natural selection is process by which individual
which are more fit for the environment survive
and reproduce
 The interaction of populations and the
environment results in changing allele
frequencies
 There are 4 different types of natural selection:
a. Stabilizing Selection
b. Directional Selection
c. Disruptive Selection
d. Sexual Selection

10.  Stabilizingselection occurs when
individuals with the average form of the
trait are most fit for the environment and
extreme traits are eliminated
 This
is the most common form of selection
and works in all populations at all times

11.  Lizard body size:
• Large lizards are easily seen by predators, but smaller
lizards cannot run as fast to escape the predators
• Mid sized lizards are most fit in the environment, so
they survive and reproduce more often, changing the
allele frequencies in the population

12.  Directionalselection occurs when
individuals with one extreme of variations
are the most fit in the environment.
 Thiscauses a gradual shift in allele
frequency to that extreme.

13.  Anteater tongue length:
• Anteaters with long tongues are most fit because
of the depth of the nests of the termites they eat.

14.  Disruptive selection occurs when both extremes of
variations are the most fit
 There is selection against the middle variations
 Ex: Limpet shells
• Dark limpets blend with bare rocks
• Light limpets blend with barnacle covered rocks
• Tan limpets are visible in both situations and get preyed
upon by birds

15.  Sexual selection is the competition for
mates within a population causing
differences to occur in the allele
frequencies of the 2 genders
 Matestend to be chosen for their
phenotypes and females tend to choose
the males.

16.  Ex: Peacocks
• Male peacocks have large tail
feathers that make it difficult to
fly and escape from predators
• Female peacocks choose males
based on their tail feather length
and fullness
• Over time males with larger tail
feathers reproduce more
causing large tails to be selected
for
• Sexual Selection in Peacocks (3
min.)

17. In evolutionary
biology, adaptive
radiation is the
evolution of
ecological and
phenotypic diversity
within a rapidly
multiplying lineage.

18.  Coevolutionary
relationships mainly
occur between
plants and
herbivorous insects
and between plants
and pollinating
insects.
 Mutually beneficial
relationship.

19. When organisms evolve similar
(analagous) structures or
functions even though their
evolutionary ancestors are very
dissimilar or unrelated.
Example:
The complex eyes of vertebrates,
cephalopods (squid and octopus),
cubozoan jellyfish, and
arthropods (insects, spiders,
crustaceans) evolved separately,
but all perform the function of
http://images.sciencedaily.com/2009/06/0
vision
90601182828-large.jpg
http://jeffvrabel.files.wordpress.com/2011/08/wolf-spider-5-29-08-
7eyes.jpg

20.  Look at the cladogram
at the right. What
conclusions can be
drawn about the
relationship between
humans and chimps?

21.  Note that this diagram
is also a timeline. The
older organism are
located on the bottom
of the tree.
 The four descendents
at the top of the tree
are DIFFERENT
species. This is called
SPECIATION.

22.  Branches on the tree represent
SPECIATION, the formation of a new
species.
 The event that causes the speciation is
shown as the fork of the “V”.

23.  Did humans evolve from
chimps? No
 What familial relationship is
a good description of the
relationship between
chimps and humans?
Distant Cousins
 Are humans more highly
evolved than chimps?
 NO- since the lineage is
split, each species has
evolved unique traits.

24. With 98.4% similar genetic
sequences chimpanzees are both a
link to Kingdom Animalia and our
kin.
Anima: James Balog
images used with permission. http://www.jamesbalog.com/