Download unit 5h.1 5b.4 genetics evolution variation

Unit 5: Genetics,
evolution & biodiversity
5H.1 & 5B.4 Genetics &
evolution; variation
By Mr. Wilson
Variation
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Variation can be thought of as the
basis for evolution.
May be caused by inherited genes
(heritable variation) or by the
environment (non-heritable
variation).
Heritable variation is the most
significant in evolution.
Origins of variation
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During meiosis of gametogenesis:
Independent assortment of
chromosomes (sometimes called random
assortment or random segregation).
Crossing over
Mutation
Sexual reproduction:
Fusing of random gametes in
populations.
Fusing of 1 of 2 gametes at each
fertilisation (4 possible outcomes).
Discontinuous variation
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For a particular characteristic there
are discreet/distinct groups of 2 or
more types with no intermediates.
Examples – ABO blood group, sex.
Is usually ‘MONOGENIC’, depending
on one gene, but modern science
suggests that this may not actually
be the case in many examples.
A limited number of phenotypes are
possible.
Discontinuous variation
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There are no
intermediate forms
so data about
discontinuous
variation is usually
shown using a
SIMPLE bar chart.
Give another
example.
Continuous variation
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Where variation between individuals
for a given characteristic varies along
a range and there are many
intermediate forms.
Examples – Height, weight, palm
span.
Caused by the combined effect of a
number of genes – POLYGENIC.
Continuous variation
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Under normal
conditions a
frequency
distribution graph
will show a
NORMAL
DISTRIBUTION.
What factors may
cause a more
random
distribution?
Discontinuous and continuous
variation.
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Which of these types
of variation is more
strongly affected by
ENVIRONMENTAL
factors?
Phenotype variation
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Both genes and the environment can
interact to produce phenotype variation.
Examples – Genes for being tall, but poor
nutrition (environmental factor) means
you don’t get that tall.
Pea plants – Dwarf & tall varieties (genes
& discontinuous variation), but a range of
heights in each group due to nutrition,
sunlight, competition etc. (environment &
continuous variation).