Download Natural Selection - This area is password protected

Natural Selection
S
Noadswood Science, 2011
Wednesday, May 24, 2017
Natural Selection
S To understand how natural selection can lead to evolution
Natural Selection
Mach each statement to its title…
1.
2.
All living things in a species are not the
same
There is not enough food or space for all
of them
3.
Some individuals have features which help
them survive
4.
They are more likely to have offspring –
more of the next generation have the
useful feature
A. Competition
B.
Survival
C. Variation
D. Reproduction
Natural Selection
1.
Variation – all living things in a species are not the same
2.
Competition – there is not enough food or space for all of them
3.
Survival – some individuals have features which help them
survive
4.
Reproduction – they are more likely to have offspring – more of
the next generation have the useful feature
Variation
S Each species has individuals showing variation (they have slight
differences) if reproduction is sexual
Competition
S Between and within a species there is competition (e.g. for food;
water; space; mates; shelter etc…)
Get off my land
Adaptation
S The better adapted individuals are more likely to survive (better at
living within their environment) – survival of the fittest
Yum yum
I’m hungry
Reproductively Successful
S These survivors are more likely to pass on their genes, so their
offspring are more likely to express the beneficial traits
You’ll all be nice
and tall
Evolution
S The basic idea behind the theory of evolution is that all the
different species have evolved from simple life forms
S These simple life forms first developed more than three billion
years ago - the Earth is about 4.5 billion years old
Natural Selection & Evolution
S The theory of evolution states that evolution happens by natural
selection: S Individuals in a species show a wide range of variation (due to
differences in genes)
S Individuals with characteristics most suited to the environment
are more likely to survive and reproduce
S The genes that allowed the individuals to be successful are
passed to the offspring in the next generation
Natural Selection & Evolution
S Individuals that are poorly adapted to their environment are less
likely to survive and reproduce, meaning that their genes are less
likely to be passed to the next generation
S Given enough time, a species will gradually evolve…
Mutations
S Mutations occur when an organism develops a new characteristic
that no other member of the species has had before – e.g. someone
being born with blue hair
S Some mutations are beneficial, some are neutral, but most are
non-advantageous
S A mutation is a change in a gene, DNA or chromosomes in a cell
which leads to genetic variation (mutations usually occur due to
errors during DNA replication)
Mutations
S DNA exists as two helical strands held together through the base
pairs by hydrogen bonding: -
S DNA mutations: substitution; deletion; insertion; and inversion
Mutations
S Each gene is the instruction for
making one protein
S Sometimes a mistake is made
when the gene’s DNA is copied
S The gene may code for a
different protein
S Mutations do happen naturally,
but they can also be caused by
some chemicals, and ionizing
radiation
Useful Mutations
S Most mutations do not help the organism – the different protein
that is made cannot do its job well
S However a very small number may help the organism survive in
some environments, e.g. bacteria with mutations that make them
resistant to certain antibiotics such as MRSA
S Sickle-cell anaemia is a serious blood disease:
people with two copies of the disease allele can
be very ill, but people who carry just one copy
of the allele have protection from malaria
increasing their chances of survival in
countries where malaria is common
Evolutionary Evidence
S Evolution is difficult to observe because it usually takes many
years to happen
S This is one reason why the theory of evolution is still a theory, not
a law – since no-one was around millions of years ago to make
observations, take notes and carry out experiments, evolution
cannot be proved in the usual scientific sense
S However, rapid changes in species have been observed that
support the theory…
Antibiotic-Resistant Bacteria
S
Microorganisms such as bacteria and viruses reproduce very rapidly and
can evolve in a relatively short time
S
The bacterium E. coli can have its DNA damaged or changed during
replication, and most of the time this has no effect, or causes the death of
the cell
S
Occasionally, the mutation is beneficial - for the bacteria, e.g. allowing
resistance to an antibiotic
S
When that antibiotic is present, the resistant bacteria
have an advantage over the bacteria that are not
resistant, so these reproduce more proficiently
passing on the resistance to future generations
Peppered Moths
S
Before the industrial revolution in Britain, most peppered moths were of the
pale variety (they were camouflaged against the pale birch trees they rest on)
S
Moths with a mutant black colouring were easily spotted and eaten by birds,
giving the white variety an advantage, and they were more likely to survive to
reproduce
S
Airborne pollution in industrial areas blackened the birch tree bark with soot
meaning that the mutant black moths were now camouflaged, while the white
variety became more vulnerable to predators
S
This gave the black variety an advantage, and they were more likely to survive
and reproduce – over time, the black peppered moths became far more
numerous in urban areas than the pale variety – natural selection directly
influenced by man
Peppered Moths
The pale peppered moths
camouflage well against
the pale birch tree
The darker peppered
moths camouflage well
against the blackened
birch tree
Peppered Moths Experiment
1.
Cut 10 small pieces of white and 10 small pieces of black paper
2.
Place them on a large piece of white paper
3.
Cover your eyes with a scarf or jumper so you can just see
through (this is more realistic as the peppered moth’s main
predators don’t have eyesight as good as us)
4.
Pick off 10 pieces of paper (the ones easiest to find)
5.
Record how many are white / black
6.
Now repeat this using black paper
S
What have you found and what
conclusions could your draw from this?
Natural Selection – Rats
S Warfarin is used as a rat poison – put the statements in order to
show how natural selection has allowed some rat populations to
become resistant to this original poison…
Natural Selection – Rats
The mutated gene is passed on and is
common in the rat population
The resistant rats have a better chance of
surviving and reproducing
A mutation in a rat’s sex cells make its
offspring resistant to warfarin
People use warfarin to kill the rats
The number of resistant rats increases
with each generation
The resistant rats breed and pass their
features on
Warfarin kills most rats
Mutations are a change in the genetic
code
Mutations may happen when DNA is
copied in the cell
Mutations can be caused by some
chemicals or ionizing radiation
Natural Selection – Rats
The resistant rats have a better chance of
surviving and reproducing
People use warfarin to kill the rats
Warfarin kills most rats
The resistant rats breed and pass their
features on
Mutations may happen when DNA is
copied in the cell
A mutation in a rat’s sex cells make its
offspring resistant to warfarin
Mutations can be caused by some
chemicals or ionizing radiation
The mutated gene is passed on and is
common in the rat population
Mutations are a change in the genetic
code
The number of resistant rats increases
with each generation
Adam & Eve
S Adam & Eve existed – they just never met!