Chapter 7 Variation (AQA) Revision Notes

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Biology Chapter 7Roisin Delaney
Differences in characteristics in organisms.
Interspecific Variation
Differences between different species.
Intraspecific variation
Differences between members of the same species.
The environment and genetics both cause variation.
Genetic differences
Variety in asexual reproducing organisms can only be increased by mutation. Sexually reproducing
organisms, in contrast, increase variation by all three methods (below). It follows that populations
of sexually reproducing organisms are more carried than asexually reproducing organisms.
These sudden changes to genes and chromosomes may, or may not, be passed on to the next
The special form of nuclear division forms the gametes. This mixes up the genetic material before
it is passed into the 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 gamete fuses with which at fertilisation is a random process
further adding to the variety of offspring two parents can produce.
This involves taking measurements of individuals in a population. It is important to avoid bias
where individuals are unrepresentative and also to avoid chance where an individual is total
unrepresentative of the group. To do this sampling should be random (use a random number

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Biology Chapter 7Roisin Delaney
chart). The larger the sample size the more accurate and more representative it will be, and
statical tests can show it and is relevant.
Types of variation
Continuous Discontinuous
Where there is a range of characteristics from Limit options for characteristics
one extreme to another.
Height/weight Gender/blood group
Influenced by the environment. Not influenced by the environment.
Lots of genes involved. 1 or 2 genes.…read more


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