A mind-map to help with the basics of variation. Hope this helps :)

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  • Variation
    • Causes of variation
      • Environmental factors
        • Plant growth is affected by the amount of minerals available in the soil.
        • Identical twins are genetically identical - they have the same alleles, so any differences between them will be due to the environment.
        • The appearance (phenotype) of an individual is also affected by the environment.
        • The fur colour of Himalayen rabbits is affected by temperature.
        • Be careful when drawing conclusions about the cause of variation.
          • Scientists draw conclusions based on the information they have until new evidence challenges, i.e. overeating & antioxidants.
      • Variation is often a combination of genetic and environmental factors.
        • No two individuals are exactly alike.
      • Genetic factors
        • You inherit your genes from your parents, this means genetic variation is inherited.
        • All members of a species have the same genes.
          • But individuals within a species can have different versins of these genes - alleles.
            • The alleles an organism has make up its genotype.
              • Different genotypes result in variation in phenotype - the characteristics displayed by an organism, i.e. eye colour.
      • Variation exists between all individuals.
      • Interspecific - the variation that exists between different species.
      • Intraspecific - the differences that occur within a species.
    • Investigating variation
      • Standard deviation
        • When all the values are similar the graph is steep so standard deviation is small.
        • When all the values vary a lot the graph is fatter so standard deviation is large.
        • The standard deviation tells you how much the values in a single sample vary.
      • Describe data
        • General trend
        • Specific data
        • Draw conclutions
      • mean value = average
        • Can be used to tell if there is variation between samples.
      • To study variation you've got to sample.
        • Has to random
          • Not biased
          • To ensure variation isn't by chance.
            • Analyse results statistically.
      • Bell-shaped graph = normal distribution.


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