as variation

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Variation Differences amongst organisms

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Page 1: As variation

Variation

Differences amongst organisms

Page 2: As variation

Learning objectives To define continuous

variation To define discontinuous

variation To understand which two

factors contribute to variation.

To understand that continuous exposure to selection pressures causes permanent adaptations.

Page 3: As variation

Why do people vary so much? Every male has the potential

to make 8 million different combinations of chromosome in their sperm

The same is true of women and eggs.

So altogether a couple can have a maximum of 64 million genetically different children!

No wonder there are so many variations in humans

Sometimes genetic mutations cause variation when egg or sperm are formed.

Page 4: As variation

There is variation within species With some species like

humans it easy to see, with others. E.g. panda’s its not so obvious.

The variations are caused by the individuals genetic make up (allele pairings)

These influence everything, from the enzymes it makes to the colour of its fur/hair etc,

Failure to make a particular enzyme often causes a disease or dietary disorders in a species.

Page 5: As variation

There is variation between species Lots of variation between

organisms is what makes species different species!

They end up isolated genetically, reproductively and/or geographically making them so different that they are classified as a different species.

Geographical isolation is sometimes referred to as Allopatric

Differences between species can be less than you think: there is only 4% difference between humans and the chimpanzee

Giraffe and Okapi (sympatric)

Page 6: As variation

Continuous variation Is variation in a species in

which there are extreme measurable examples (e.g. very short/very tall and lots of intermediate values in between

It usually forms a bell shaped curve (called a normal distribution) especially if a large sample is taken.

Continuous variation is usually a polygenic phenomenon (i.e lots of genes control it)

The environment often influences it too.

Page 7: As variation

Discontinuous variation These are very distinct

differences which cannot be measured on a scale e.g. eye colour, blood group, attached or unattached earlobes etc.

There are no intermediate values

They are usually coded by one gene pair (alleles) only.

Page 8: As variation

Environmetal influences These combined with your genes can affect

continuous variation Examples are: Diet Exercise Diseases you catch Alcohol consumption Smoking and drug abuse Education

Page 9: As variation

Environmental Influences are not passed on. If you break an arm and your arm ends up

deformed. If end up massively obese because

you regularly eat McDonalds If you get rickets and have bow legs If you dye your hair These characteristics will not be passed on to your

children because they are not genetic, they are caused by your interactions with the environment.

Page 10: As variation

Adaptations to the environment The features which an organism has must be well

suited to its environment. If not it risks extinction Adaptations fit into 4 main categories:

Structural

Physiological

Biochemical

Behavioural

Page 11: As variation

ExamplesAdaptation Rhizobium Venus

flytrapFennec fox

Structural Nitrogenase (fixes nitrogen)

Adapted leaves form traps

Large ears

Behavioural Moves through soil and into roots

Insects trigger leaves to trap it

nocturnal

Physiological Exchanges amino acids for energy molecules with host plant

Secretes enzymes onto dead insects

Ears have large surface area to lose heat

Page 12: As variation

Examining Structural Variation

Look at the three skulls What structural

variations do you notice?

How do you think these adaptations help the hominid survive better in its environment?

Page 13: As variation

Questions

Define the term variation (give one example in humans) 2 marks

Explain the difference between variation between species and variation within species 2 marks

What shape is a normal distribution typically found in continuous variation? 1 mark

How is continuous variation different to discontinuous variation 2 mark

Give one example of an adaptation in a species and how it fits the organism to its environment 2 marks