National 5

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National 5

• Adaptation, Natural Selection Evolution

Mr G Davidson
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Mutations

• A mutation is the random changing of an
  organisms genetic material.
• Mutations are very rare and they occur randomly.
• This mutation can cause a change in phenotype of
  an organism, and if it does, the individual is
  said to be a mutant.

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Mutations

• Mutations can be brought about by exposing cells
  to mutagenic agents such as
• Radiation
• UV light
• Gamma rays
• X-rays
• Chemicals
• Colchinine
• Caffeine
• Mustard gas
• Chemicals in tobacco

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Mutations

• Mutations can cause changes that leave the
  organism better off than it was before.
• These are called advantageous mutations.
• These are very rare but they do increase
  variation within the species.

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Mutations

• There are some plants which have more than one
  set of chromosomes.
• This is caused by spindle fibre failure.
• They are called polyploids and they are normally
  superior to the normal variety
• Larger fruit
• Greater yield
• Better disease resistance

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Mutations

• Other mutations can have no effect on the
  organism and these are called neutral mutations.
• These mutations can occur in parts of the DNA
  which dont code for proteins.
• If they do occur in the DNA which codes for
  protein, the change is so minor that it has no
  overall effect.

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Mutations

• There are, however, mutations called
  disadvantageous mutations.
• If the mutation happens in genes which code for
  essential enzymes, the organism may be in danger
  of not surviving.
• They may even lead to genes being lost.
• Examples of such mutations include cystic
  fibrosis and sickle cell anaemia.

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Variation

• Mutations are the only source of new variation.
• Without them all organisms would be homozygous
  and there would be no variation.

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Variation

• Because there is variation, the organisms with
  the advantageous mutations survive and pass them
  on to the next generation.
• This is what causes evolution.
• These variations are called evolutionary
  adaptations and they allow organisms to cope
  better with environmental changes.

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Adaptations

• There are biomes which make life very difficult
  and if organisms can adapt to live in these
  places, they will incur less competition.
• Deserts are a good example, where it is very arid
  and hot during the day, but very cold at night.
• There are some organisms which have adapted to
  living in deserts.

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Adaptations

• There are two types of adaptation organisms can
  show
• Behavioural adaptations where the organism adapts
  its behaviour in order to cope.
• Physiological or structural adaptations where the
  organisms body has adapted through evolutionary
  changes.

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Desert Rat

• The desert rat or kangaroo rat is a small mammal
  which shows both types of adaptation in order to
  survive in the desert.
• Behavioural adaptations include the rat remaining
  in an inactive state in underground burrows
  during the heat of the day in order to conserve
  water.
• They become active at night.

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Desert Rat

• Physiological adaptations include
• dry mouth and nasal cavities which reduces the
  amount of water lost when breathing.
• No sweating.
• Very long kidney tubules to improve the
  reabsorption of water.
• They produce very concentrated urine.

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Camels

• Camels have a number of physiological adaptations
  to help them survive in the desert.
• Very thick fur on top of the body to protect it
  from the heat of the sun.
• The have fat in the hump which can be metabolised
  to release water.
• Large feet helps to spread their weight and
  prevent them sinking into the sand.

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Desert Plants

• Plants also have a huge range of adaptations to
  help them to survive in very dry areas.
• They have huge root systems that can go very deep
  into the ground to find water.
• The leaves are reduced to spines to reduce the
  surface area through which water could be lost.
• The stems are fleshy and capable of storing water.

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Natural Selection

• All species of organism produce offspring in
  order to maintain the species.
• They all produce more offspring than is required
  to do so.
• This results in some of these offspring being
  weeded out before they can reproduce.

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Natural Selection

• This is called natural selection or survival of
  the fittest.
• The best adapted individuals will survive at the
  expense of the weakest individuals.
• It is natural variation which causes these
  differences between individuals.

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Natural Selection

• Organisms are subjected to selection pressures
  such as
• Starvation
• Low disease resistance
• Lack of space
• Slower (cannot escape from predators)
• Competition

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Natural Selection

• Natural selection is constantly changing the
  characteristics of organisms.
• This happens over an extended period of time to
  accommodate the changing environment.
• Examples include
• Peppered moth
• Antibiotic resistant bacteria.

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Speciation

• A species is a group of organisms which can
  interbreed and produce fertile offspring.
• Speciation is the development of a new species.
• This is something which happens over a very long
  period of time.
• It starts when a large group of organisms of the
  same species become separated into 2 or more
  groups.

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Speciation

• This may be caused by
• Geographical barriers such as oceans or mountains
• Ecological barriers caused by changes in abiotic
  factors such as temperature, pH, water, etc.
• Reproductive barriers such as non-fertilisation,
  wrong courtship behaviour, etc.

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Speciation

• Once the main group have been split, mutations
  occur within the smaller groups resulting in new
  alleles.
• This can alter the phenotype of the organisms.
• As time passes the environment applies slightly
  different selection pressures on the population
  and the mutant forms survive better.

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Speciation

• These individuals then survive to reproduce and
  pass on the new alleles.
• The individuals without the new alleles will be
  selected against.
• This results in the characteristics of the
  population changing.

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Speciation

• After a long time, even if the barrier is now
  removed, the 2 populations will differ from each
  other so much that they are no longer able to
  interbreed and produce fertile offspring.
• Therefore, they are now separate species.

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Speciation
Large population of organisms interbreeding and
producing fertile offspring
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Speciation
Same environment as before
Wetter environment than before
Large population of organisms get separated by a
body of water and can now no longer interbreed.
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Speciation
Same environment as before
Mutant forms begin to appear
Over a long period of time some of the organisms
mutate and these mutant forms survive better in
the wetter environment because they have bigger
feet which stops them sinking.
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Speciation
Same environment as before
Mutant forms show an advantage and survive
better
Over a long period of time the mutant individuals
numbers increase because they are surviving in
the wetter environment
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Speciation
Same environment as before
New form of organism is now the dominant form
Over a long period of time there are now 2
different species.
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Speciation
If the body of water now dries up and these 2
varieties can mingle, they are no longer able to
interbreed and produce fertile offspring.
Two distinct species now exist.