Transcript Variation

KS4 Biology
Variation
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Contents
Variation
What is variation?
Causes of variation
Classifying variation
Investigating variation
Variation quiz
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Variation between species
Variety is the spice of life!
Variation is the differences between different living things.
How many differences between living things can you name?
What causes the differences between species?
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Variation between species
Species are different because their genes are different.
Genes are the biological code for different characteristics.
Humans have human genes.
Bananas have banana genes.
Gerbils have (yes, you’ve guessed it) gerbil genes!
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Variation within species
The current population of planet Earth is more than
six thousand million people!
No two people are exactly the same. How is this possible?
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Variation within species
Members of the same species also show variation.
These differences are called characteristics.
How many human characteristics can you think of that
show variation?
What causes each person’s unique characteristics?
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Contents
Variation
What is variation?
Causes of variation
Classifying variation
Investigating variation
Variation quiz
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Spot the family likeness
Members of the same family often look similar.
Mum
son
Dad
daughter
Which parent do these children look more like?
If the son grows up to have children who might they look like?
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Inherited characteristics
Why do members of the same family look similar?
Mum
son
Dad
daughter
Humans, like all living things, inherit characteristics from
their parents. How are characteristics passed on?
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Inherited characteristics
This newborn baby’s characteristics are passed in
the genes it has inherited from its parents.
Like all babies, this little boy carries a unique set of genes,
half from his mother and half from his father.
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Making faces
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Causes of variation
People are different because they inherit different
characteristics from their parents.
But are your characteristics only affected by your genes?
What else will influence the characteristics of this baby
as he grows up?
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Causes of variation
When he gets older, this baby might support a different
football team (like Fulham) or not even like football.
Your upbringing and the environment in which you live
also affect how you turn out as an adult!
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Causes of variation
Your unique characteristics are caused by:
- the unique set of genes you have
inherited from your parents
- the environment in which you have
developed.
Differences in some characteristics are
due to a combination of both inherited
and environmental factors.
Name three examples of this type of
characteristic.
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Causes of variation
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Variation in plants
Plants inherit characteristics through their genes just
like humans and other animals.
What characteristics have these plants inherited?
Are plants also affected by their environment?
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What causes variation in plants?
Plants are affected by four key environmental factors.
Can you name them?
water
sunlight
temperature
nutrients in soil
Plants are affected by their environment in a big way.
With a little more moisture, light or warmth the size of a
plant can double. (Imagine if that happened to us!)
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What causes variation in plants?
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Contents
Variation
What is variation?
Causes of variation
Classifying variation
Investigating variation
Variation quiz
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How to classify variation
Characteristics can be classified in different ways.
How would you categorize variation in eye colour?
Could you categorize variation in height in the same way?
Variation in eye colour can be easily categorized in distinct
groups. You either have a certain eye colour or you don’t.
Height variation doesn’t fall into separate groups, as it covers
a range of values. Your height changes as you grow.
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How to classify variation
Characteristics can be classified into two types:
discontinuous variation
A feature that can be measured and given a value from
a range of values shows
.
A feature that cannot be measured but is one of a few
distinct options shows discontinuous variation.
Which type of variation are eye colour and height?
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Continuous or discontinuous?
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Continuous variation
This type of feature varies over
a continuous range of values.
Examples of continuous variation
include mass, height, skin colour,
intelligence and leaf area.
Continuous variation is due to the
combined effects of genes
and the environment.
?
Bar chart to show the range of
masses in a rugby team
number of rugby players
What is
6
5
4
3
2
1
0
70
1
80
90 100 110 120 130
mass (kg)
Does this mean the value of such a feature is fixed
or can it change?
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Continuous or discontinuous?
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Discontinuous variation
What is discontinuous variation?
Examples of discontinuous
variation include blood group,
natural eye colour and inherited
diseases.
Bar chart to show the frequency
of blood groups in a rugby team
number of rugby players
This type of feature can only
be one of a few distinct options.
Either you have this type of
characteristic or you don’t.
6
5
4
3
2
1
0
O
A
B
blood group
AB
Discontinuous variation is the result of genes only.
Does this mean the value of such a feature is fixed?
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Continuous or discontinuous?
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Contents
Variation
What is variation?
Causes of variation
Classifying variation
Investigating variation
Variation quiz
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Curious about variation
How do we know about inherited variation and how it works?
Meet Gregor Mendel, the first person to trace patterns
of characteristics and predict how they were passed on.
Gregor Mendel
1822–1884
Surprisingly, Mendel was not a scientist, but a monk who
lived in Czechoslovakia (now called the Czech Republic).
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Mendel’s experiments
Mendel was inspired by walking in the monastery garden.
He became curious about variation in plants and how
characteristics were passed on to new generations.
Another surprising fact about Mendel is that for his
ground-breaking work on variation he carried experiments
out on the humble garden pea!
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Mendel’s experiments
Mendel chose to experiment on pea plants for two reasons:
1. They could be easily grown in large numbers.
2. Their reproduction could be controlled.
Over a period of seven years he experimented on more
than 28,000 pea plants!
Why was the pea plant a good choice for his experiments?
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Mendel’s experiments
Mendel studied several pea characteristics including:
- pea shape
(smooth or wrinkly)
- pea colour
(yellow or green)
- pod shape
(inflated or constricted)
- pod colour
(yellow or green)
- stem length (tall or short)
All these characteristics showed discontinuous variation.
Why did this make them easier to study?
Mendel also investigated one characteristic at a time.
Why was this important for his experiments to be successful?
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Smooth and wrinkly peas activity
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Mendel’s results
Mendel’s investigations into seed shape (smooth or wrinkly)
produced the following results:
x
parents:
first
generation:
100%
second
generation:
75%
dominant
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cross-pollination
x
self-pollination
25%
recessive
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Mendel’s conclusions
Mendel published his work in 1866 and made several
conclusions about inheritance:
 Certain traits can be dominant or
recessive. Recessive traits may
not show but can still be passed on.
 Certain traits can be inherited in
predictable patterns.
 Inherited traits are passed on as
bits of information called “factors”.
What are these “factors” now called?
Mendel did not know it but he had predicted the existence of
genes more than 40 years before genes were discovered!
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Father of Genetics
Mendel’s work on the humble pea laid the foundations for
modern genetics.
Unfortunately, Mendel published
his research in an obscure journal
and the importance of his work
was not recognized during his life.
Scientists rediscovered Mendel’s
work in 1900, sixteen years after
he died!
Today, Mendel is famously known
as the “Father of Genetics”.
Why is he given this grand title?
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Contents
Variation
What is variation?
Causes of variation
Classifying variation
Investigating variation
Variation quiz
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Variation multiple-choice quiz
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