Variation

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  • Variation
    • Sampling
      • Sampling involves taking measurements of individuals, selected from the population of organisms which is being investigated.
      • A sample should be representative of the general population
      • Sampling bias - investigators may be making unrepresentative choices, either deliberately or unwittingly
      • Chance - even if the sample is not bias the individuals chosen may by pure chance not representative
      • Use a larger sample - the bigger the sample the smaller the probability that chance will influence the results
      • Use random sampling
      • Analysis of the data collected - use statistical tests to find out how much chance has influenced the results
    • Causes of Variation
      • Could be due to genetics
        • Mutation - these may or may not be passed on to future generations
        • Meiosis - this forms the gametes. It mixes up the genetic material before it is passed into the gametes which are all different
        • Fusion of gametes - in sexual reproduction the offspring inherit characteristics from each parent and are therefore different from both of them.
      • Environmental influences
        • The environment exerts an influence on all organisms. This influences the way the organisms genes are expressed.
        • Environmental influences include climatic conditions temp, rainfall, sunlight, soil conditions, pH and food availability.
      • In most cases variation is caused by both genetics and the environment, it is hard to tell the exact cause of variation.
    • Graphs
      • Genetic variation can be shown using a bar chart as there tends to be only a distinct few forms. for example the ABO blood grouping system.
      • Variation due to the environment can be shown using a frequency graph as there are a number of factors influencing something.
    • Creating a distribution curve
      • The mean is the measurement of the maximum height of the curve. mean is useful when comparing data
      • Standard deviation is a measure of the width of the curve. It gives an indication of the range of values either side of the mean.

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