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All organisms vary from one another ,
even within a species.
Variations in living organisms has both a
genetic and environmental basis.
• Name a feature which is due to genetics only
• Name a feature which is due to environment only
• Name a feature which is due to both
There are 2 types of variation in organisms:
1. Discontinuous variation
These characteristics
fall into groups
for example
your blood group
can be A, B, AB or O
Another example includes whether you can or
can’t roll your tongue.
Discontinuous characteristics tend to be the result
of genes only.
Bar graphs are used to display data gathered about
discontinuous characteristics.
The bars are separated from one another by a space
2. Continuous variation
Characteristics are between 2 extremes
Height is an example of discontinuous variation
Continuous characteristics tend to be
the result of both genes and the
Factors such as the availability of
food, water, and disease will affect
the eventual height a person is able
to grow to.
Both of these maple trees are 30 years old.
The one on the left is a bonsai, it’s roots have
been pruned to restrict growth. However, it has
the genetic potential to reach the same height
as the tree on the right.
Histograms are used to display data
gathered about continuous variation.
The bars are not separate from one
another, but show a continuous range.
The histogram shows that there are few
very small or very tall people; most are of
the middle heights.
This characteristic bell shape is known as
a normal distribution.
1. Write a title for the graph.
•The height of men compared to women
2. Use the graph to describe two differences between
the heights of men and women.
•The average height of men is more than women.
•The range of heights of men is bigger than women.
•There are fewer men of average height than women.
3. How would you gather reliable, valid data to produce
this graph?
•Large sample of men and women (>1000)
•Same age
•Same ethnic origin
Sexual reproduction results in
genetic variation due to
meiosis, fertilisation and
Variation and selection
may lead to evolution or
Organisms that can adapt
to a changing environment
evolve, those that don’t
become extinct.
• Organisms within a species have different
features or phenotypes
• In large populations organisms will compete
for resources (food, space, mates)
• A change in the environment occurs
• Organisms with the best adapted features
are more likely to survive
• These organisms reproduce, passing on
their genes to their offspring
• The new population gradually changes to
suit the environment.
• A population of disease causing bacteria has many
mutations. One mutation may give resistance to
an antibiotic such as penicillin.
• When someone is given penicillin to kill an
infection of these bacteria, the ones without the
mutation will die, but the antibiotic resistant ones
will survive and reproduce. All of their offspring
will be resistant to the antibiotic and so will
continue to multiply.
• A different antibiotic must be used to kill these
“ I have called this
principle by which
each slight
variation, if useful,
is preserved,
by the term
Natural selection.”
– Charles Darwin from
“The Origin of
• Natural selection
over thousands of
years is thought to
be the driving force
behind evolution in
which organisms
gradually change
from one form to