Transcript File

Adaptations,
Natural Selection
& Evolution
1. Mutations
•
MUTATION = change in structure or composition
of an organism’s DNA
•
MUTANT = an organism that displays the
genotypic mutation in its phenotype
•
Mutations are random events that tend to be
recessive so appear in a low number of the population
•
Mutations are the source of new variation
•
Variation is the differences between members of a
species
•
Mutagenic agents that can increase mutation rates
There are 2 main categories of mutagenic agents:
•
Chemicals & Radiation
Chemical Mutagenic Agents: Radiation Mutagenic Agents:
- Mustard Gas
- X-rays
- Colchicine
- UV Light
- Caffeine
- Gamma Rays
- Formaldehyde
Mutations can be:
•Advantageous for the organism- the
mutation has caused the mutant to be
better than the original organism. It is the
source of new variation.
• E.g. polyploidy in plants
•Disadvantageous for the organism- the
mutation causes harm to the organism
• E.g. cystic fibrosis/sickle cell
anaemia
•Neutral- the mutation causes no change
to the organism, it is neither beneficial or
harmful
2. Adaptations
• An adaptation is a characteristic possessed by an
organism which makes it well suited to its environment
• Adaptations are favoured by natural selection as they
increase the individual’s chance of survival
•Adaptations can be:
• Structural
• Physiological
• Behavioural
2. Adaptations
The Galapagos Islands
lie west of South
America in the Pacific
Ocean
On these islands live
13 different species
of Finch
In order to survive, each Finch species has
adapted to occupy a particular niche (role)
2. Adaptations
Different Finch species
have:
•different beak shapes
and sizes
•different habitats/niche
Can you think which
finch lives near bark
containing burrowing
insects?
Which lives on the
ground near trees
that produce thick
walled seeds?
Bee pollinated plants
Bee pollinated flowers often have UV
colouring, invisible to the human eye
but visible to the bee.
To the bee this
is a target
signalling where
the nectar is,
and promotes
pollination.
Cacti
Succulent tissue, deep root and
superficial roots, no broad leaves.
Polar bear
Camouflaged, dark skin for
insulation, blubber, wide feet.
African Bullfrog
Uses spade-like hind-legs to burrow
away from predators.
Sea dragon
Camouflaged to protect from predators.
Camel
Elephant
3. Natural selection
• What examples of variation can you think of in
humans?
• Can you think of other examples of variation in other
species?
• An organism that is ‘struggling for survival’ means that
only the best adapted organisms will survive to pass on
their genes
• Organisms that are best adapted are said to have a
‘selective advantage’ over other members of the species
Charles Darwin
Sexual reproduction produces more
offspring than environment can support
Some weaker rabbits
die
Inherited variation is
expressed in phenotypes
Some slower rabbits
are caught
Healthiest, strongest, fastest etc survive &
breed
Poorly adapted die
More offspring produced than the environment can
support, best adapted survive to pass on genes
Poorly adapted die
Natural selection in action: The Peppered Moth
Peppered moth exists in 2 colours, light and
melanic. Each have selective advantage in
different environments.
Before the industrial revolution:
•light moths had a selective
advantage
•well camouflaged against the
lichen-covered trees, they were
better able to avoid predation
• During the 19th century pollution
killed off some of the lichens and
soot deposits caused the tree bark
to appear darker
• Light moths = no longer
camouflaged and more likely to be
eaten by birds
Light is favoured
• Dark moths had a greater chance
of reproducing and passing on the
alleles that made them dark
Melanic is favoured
• caused a gradual increase in the
proportion of dark moths until light
moths became very rare in
industrial areas
•The moth populations in these
areas had evolved
• This change from predominantly
light to dark forms in industrial
areas is called industrial melanism
Note that this change was not due to pollution making the moths
darker. The dark variety had always existed in small numbers, but
only had a selective advantage when the selection pressure changed.
Resistance to antibiotics
a. One mutant bacteria arrives
spontaneously in the population.
b. Mutant bacteria has selective
advantage and survives.
c. Resistant bacteria
reproduces to make more
resistant bacteria.
Resistance to antibiotics
d. One of these bacteria may be
resistant to a 2nd antibiotic.
e. Mutant bacteria has selective
advantage and survives to
reproduce more like bacteria.
4. Speciation
• A species is a group of organisms that can
interbreed to produce fertile offspring
• All of the members of the same species
make up a population
• the gene pool refers to the different
genes within an interbreeding population
•Speciation is the name given to the process
where two new species are formed from one
original species
4. Speciation
• Speciation requires some sort of
isolation barrier (something that causes
the original population to become
divided)
• These barriers can be:
• Geographical (seas, rivers,
mountains/deserts)
• Ecological (temperature, water
availability, pH)
• Reproductive (sex cells unable to
fuse, unsuccessful mating displays,
flowering at different times of
year
Population separated by
an isolation barrier
Different mutations occur in
each new sub-population
Variation is displayed in each new
population & natural selection
occurs where those with the
selective advantage will survive &
pass on their genes
After many generations, mutations
and natural selection changing the
gene pool of each population, even
if the isolation barrier is removed,
these sub-groups will no longer be
able to interbreed to produce
fertile offspring