AQA Biology AS Variation Unit 2

These might not include everything, so only use them as a rough guideline and you are best using your text book to fill in the gaps in your knowledge, as these notes are specific to me.

They do have all the main points included though

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Variation
Sampling
Sampling bias- The selection process may be biased. The investigators may be making
unrepresentative choices, either deliberately or unwittingly.
Chance- Even if sampling bias is avoided, the individuals chosen may be, by pure chance, not be
representative.
Causes of Variation
Genetic Differences
Mutations- these sudden changes to genes and chromosomes, may or may not be passed onto the
next generation.
Meiosis- This forms gametes. This mixes up the genetic material before being passed into gametes,
all of which are therefore different
Fusion of Gametes- In sexual reproduction the offspring inherit some characteristics of each parent
and are therefore different from both of them. Which gametes fuses with fertilisation is a random
process further adding to the variety of the offspring two parents can procuce
Environmental Influences
The environment exerts an influence on all organisms. These influences affect the way the organism's
genes are expressed. The genes set limits, but it is largely the environment that determines where,
within those limits, the organism lies.
Types of variation
Variation due to genetic factors
Where variation is the result of genetic factors organisms fit into a few distinct forms and there are
no intermediate types.
Variation due to environmental influences
Characters that display this type of variation are controlled by Polygenes. Environmental factors play
a major role in determining where on the continuum the organism lies. For example, humans which
are the same height will grow to be different heights due to environmental factors such as diet. This
type of variation is as a result of Polygenes and environment.

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