Investigating Variation.

How is variation measured?

What is sampling?

What are the causes of variation?

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  • Created by: Charlotte
  • Created on: 14-03-12 22:16

The different types of Variation.

    • one species differs from another species.
    • when members of the same species differ

Even identical twins, who are born with the same DNA, vary as a result of their different experiences.

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Making measurements.

Why is it so difficult? 

  • It is difficut to make measurements as a Biologist because they are usually measuring some aspect of a living thing, and all living things differ from each other. 
  • They cannot measure every member of the species in question, so they take samples.
  • They make averages and conclusions from this data.


  • Taking measurements from a selected proportion of the population
  • These should be, in theory, a true representation of the species we are measuring. 
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Non-representative data. Reasons why.

Sometimes a sample may not be representative of the whole population, this can be down to two main factors:

Sampling Bias:

  • Where the selection process may be biased. Eg. throwing quadrates in another direction to nettles.
  • We reduce sample bias by:
    • making the study area into a grid,
    • generate random numbers on a computer
    • take samples at the intersection of the co-ordinates.
    • Chance:
  • Even if samping bias is avoided, the individuals chosen may, intentionally or unintentionally, not be representative.
  • To reduce chance we:
    • use a larger sample to gain a more reliable result
    • use statistical tests to work out the pobability that chance will influence the data.
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Factors affecting variation.

Genetic differences:

  • Mutation
    • sudden changes in the species will be passed on to offspring.
  • Meiosis
    • special form of nuclear division forms gametes. This mixes up the genetic material before its passed into the gametes, all of which will be different.
  • Fusion of gametes
    • in reproduction, offspring inherit some of different from both when gametes fuse its a random process which adds to the variety of offspring the parents can produce.
  • Asexual reproduction

Environmental influences

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