# 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.

• INTERSPECIFIC:
• one species differs from another species.
• INTRASPECIFIC:
• 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.

SAMPLING:

• 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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