Transcript Variation & Natural Selection

EVOLUTION
 Cumulative effects of change on a population through




vast periods of time
Involves a change in a POPULATION, not in
individual members
Replication of DNA ensures CONTINUITY within the
species
Recombination of genes during crossing over makes
you DIFFERENT
Genetic VARIATION provides the material on which
evolution acts
Variation
Variation: a difference or
deviation from the normal
recognized characteristic for
that species
Why is it important?
 Small differences provide the raw
material for evolution
Variation
 Variation improves the chances that a species will




survive under CHANGING environmental conditions
Variations are created from mutations and genetic
recombination and random events. (mutations are rare!)
If the mutation is “good” or helpful, it may be passed
on to future generations
Some individuals will have a better chance of
surviving to adulthood and producing offspring
Environment + Genotype = Phenotype
Example of how Variation helps in Evolution
Most deer are brown
A mutation causes some deer to be born “albino”
Usually this is bad because predators can see them more
easily
If we enter a new ice age, albino deer with have an
advantage because they will blend in with the snow
This ensures survival of deer as a species
NATURAL SELECTION
Natural Selection is….
A mechanism of evolution
where members of a
population with the most
successful adaptations to their
environment are most likely to
survive and reproduce.
Selection….
Favoring organisms best fit to a
given environment
Without VARIATION in a
population
there could be
NO
NATURAL SELECTION
There are two types
of Selection
Natural
Selection
Individuals with
the best adaptation
to the environment
will be favored and
will survive to
reproduce
Artificial
Selection
Selection by humans of
individuals with
wanted characteristics
for breeding,
OR
Do not breed
individuals that have a
trait we don’t like.
Natural selection is based on
adaptations
Adaptations:
any trait which enables an organism to respond
(adapt) to its environment and allows it to survive
and reproduce
Camouflage:
species blends
in with its
surroundings
Mimicry:
organisms looks
very similar to
another
organism
Which is poisonous
Other adaptations
STRUCTURAL
 Traits that involve the physical structure of an
organism like the beaks of birds
FUNCTIONAL
 Traits that involve functions
of an organism


Sticky tongue for predation
Enzymes to digest particular food
BEHAVIORIAL:
Inherited traits that help an organism survive
and reproduce in a given environment
examples: mating songs and courtship dances
plant movement
Two of these are Bumblebees(with stingers) and
two are Robber Flies (which also make a sound
similar to a bee).
If you were a predator, could you "bee" sure of
the difference?
Evolution
Means “change over time”
FACT:
We have seen species change
over time
Charles Darwin’s theory of natural
selection
Overproduction of offspring:
more offspring are produced than
can survive
Struggle for survival:
organisms compete with each other
for limited resources
 Other evolution theories…..
SPECIATION
SPECIATION:
The emergence of a new species
from pre-existing species
What makes a species?
Organisms that can breed and
create fertile offspring in nature
Horse
+
Donkey
=
Mule
Mules are sterile and cannot reproduce!
Horses and donkeys are different enough to be
separate species.
Allelic Frequency