Transcript Evolution - SchoolNotes

Do Now
1. Come in quietly
2. Copy the objective (To learn about
Evolution)
3. Relax and wait until class starts
4. And please don’t put the textbooks that
are on your desks on the floor.
Evolution
Darwin in a nutshell
 Individual organisms in nature differ from one
another.
 Organisms in nature produce more offspring
than can survive.
 Because more organisms are produced than
can survive, competition for limited resources
takes place.
 Since each organism is unique, each has
distinct advantages and disadvantages in the
struggle for existence.
Darwin (con’t)
 Individuals best suited to their environment
survive and reproduce most successfully. The
characteristics that make them survive are
passed on to their offspring.
 Species change over time.
 Species alive today have descended with
modifications from species that used to live in
the past.
 All organisms on Earth are united into a single
tree of life by common ancestors.
Gene Pools
 A gene pool is the
combined genetic
information of all the
members of a
particular population.
Sources of Genetic
Variation
 Mutations –
A change in sequence of
DNA. Things that can
cause mutations:
 Mistakes in DNA
 Radiation
 Chemicals
They can affect a single
base, a length of DNA or
an entire chromosome
 Genetic Shuffling –
This is basically the
genetic variation that
occurs with the
process of sexual
reproduction
(crossing over, 4n,
etc.)
Genetic Drift
 Occurs when one
portion of the
population finds a
new habitat.
 Now, there are
different types of
genes present in the
new gene pool
 This creates a new
population.
Genetic Equilibrium
 This is a situation where allele
frequencies (the amount of times a trait
occurs) stay the same.
 In order for this to happen, the following
must occur:
A. There must be random
mating
 Random mating
ensures that each
organism has an
equal chance to pass
on its genetic
information
Random Mating Allowed
No Random Mating Allowed
B. Large Population
 A large population
would limit the effect
of Genetic Drift
C. No movement into or
out of the population
 Genetically, this
would keep the gene
pool of a certain
population in tact and
totally different from
nearby gene pools
D. No Mutations
 A mutation would
alter the types and
numbers of alleles
present in the gene
pool.
E. No natural selection
 No phenotype can
have a selective
advantage over
another.
Speciation
 This is the formation
of a new species
from pre-existing
ones.
Isolating Mechanisms
 In order for speciation to occur, there must be an
isolation in gene pools between the ‘old’ species and
the newer forming species.
Reproductive Isolation
 Once the new
species has changed
enough where it no
longer can share a
gene pool with the
‘original species’,
both species are said
to be reproductively
isolated.
How does reproductive
isolation occur?
 One way is called
BEHAVORIAL
ISOLATION.
 This is when there is
a difference in
behavior (duh)
namely in courtship
rituals.
Bufo
alvarius
Bufo
cognatus
 A second way that isolation can occur is called
GEOGRAPHIC ISOLATION.
 This is where two populations are separated by
a geographic barrier.
 A third way that isolation can occur is
Temporal.
 Temporal isolation is when the two species
have a different mating season, duration, etc.
Speciation In
Darwin’s Finches:
1. Founders Arrive
2. Separation of
Populations
3. Changes in the
gene pool
4. Reproductive
isolation
5. Ecological
Competition
6. Continued
evolution
Final Important Terms
 Adaptive Radiation –
When a single species
has evolved into
several different
forms that live
successfully in
different ways
 Convergent Evolution –
When two or more unrelated organisms evolve to
look like each other.
Ex. Aquatic animals (sharks, dolphins, etc.)
 Coevolution –
Two species evolve in response to changes in each
other over time.