AQA AS Unit 2 Variation 3.2.1

This powerpoint summarises chapter 7 in the AQA biology textbook.

I used the specification, the textbook and my class notes to make this revision presentation so I hope it's useful.

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Unit 2 The Variety of Living
FACTORS…read more

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Interspecific Variation
Variation between different species.
Differences in species are mainly due to DNA
Differences between species arise due to;
The structure and sequence of genes in each organism.
The way in which the genes are expressed.
A gene can only have an impact on an organism if it
is switched on and used to make a particular protein.…read more

Slide 3

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Intraspecific Variation
Variation between members of a species.
The genotype of an organism is the genetic makeup,
the collection of alleles that the organism has
inherited from its parents.
The phenotype of an organism is the collection of
observable features that is has
i.e. Genotype + environment = phenotype…read more

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Types of intraspecific variation
Discontinuous Continuous
Variation that falls neatly Variation that can be any
into categories; one thing value within a range.
or the other. Tends to be Tends to be controlled by
controlled by single many alleles (polygenic)
alleles, which are present and environmental
or not. factors that combine to
Usually displayed as a give the phenotype.
histogram. Usually gives a normal
E.g. Blood group, ability distribution curve.
to tongue roll, ear lobe E.g. Height, mass, shoe
shape, etc. size, arm span, etc.…read more

Slide 5

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Deviation and
Standard deviation
refers to the spread of
the data around the
mean and is shown in
the width of the curve.
The mean is the
arithmetic average.…read more

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Causes of Variation ­ Genetic
1. Sexual reproduction involves the production and fusion of gametes.
Gametes are produced by meiosis. Variation occurs during meiosis
Cross-over events ­ can reshuffle genes producing new combinations.
Independent assortment of chromosomes ­ during meiosis this reshuffles maternal
and paternal chromosomes thus producing new combinations of alleles.
The joining of gametes during fertilisation also introduces variation
in two ways:
Random mating ­ when this occurs between individuals, two different sets of genes
are brought together.
Random fertilisation ­ each fertilisation event is a random event and which pair of
gametes fuse is a matter of chance.
2. Mutation ­ a change in the genetic material of an organism. A
gene mutation is a change in the base sequence of a gene, which
will probably result in a change in the amino acid sequence. In
turn, this may affect the overall shape and therefore the
functioning of the protein.
Mutation is the ultimate source of all variation.
Mutation creates new alleles.…read more

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