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Today we are covering from the
specification:
Parents
A
B
C
Progeny (children)
1
2
3
Parents
A
B
Johnny Ball
1
C
Progeny (children)
2
3
Zoe Ball
Parents
A
B
C
John Lennon
Progeny (children)
2
1
Julian Lennon
3
Parents
A
B
C
Kirk Douglas
Progeny (children)
1
2
Michael Douglas
3
How did you do?
• You were able to match the parents to the
progeny, not only through similarities but also
differences.
• These are differences within a species.
• This is known as intraspecific variation.
Variation within species
• This relies upon mutations within a species.
• This variation is acted upon by selection
pressures.
• Only the fittest individuals will survive to
breed.
• This is the way that evolution via natural
selection operates.
What is interspecific variation?
• These are differences between different
species.
e.g. the differences between a zebra and a horse.
Variation
• Variation is the existence of
variety and differences
within and between species.
• On the surface organisms
may look identical but on
closer inspection show a
great deal of variation in
their genetics, behaviour
and lifestyles.
Measuring variation
• Measuring variation can be a real problem for
biologists.
• This is because they are measuring some
aspect of a living organism and all living
organisms are different.
• There are also many individuals of each
species – it would be difficult to take
measurements from each one.
Measuring variation - Sampling
• Sampling can help to overcome this problem.
Measuring variation - Sampling
• Sampling can help to overcome this problem.
What do you understand the term
“sampling” to mean?
Measuring variation - Sampling
• Sampling involves taking a selection of
individuals from the target population (the
population being investigated).
• These individuals will represent the
population as a whole.
• The sample should be unbiased and
representative of the whole population.
Measuring variation - Sampling
• However, sampling is not always reliable.
Why not?
The problem with sampling
• Sampling Bias – The selection process may be
biased. The investigators may be making
unrepresentative choices, either deliberately
or unwittingly.
• Chance – Even is sampling bias is avoided, the
individuals chosen, by pure chance, may not
be representative.
Random sampling
can help with these
problems.
But how is this
done?!
Using a large
sample size and
appropriate
analysis of data
collected will also
help!
Genetic Variation
• Every person on Earth has their own unique
genetic make-up (unless they are an identical twin).
• Most of our 25,000 genes are controlled by
more than 1 allele.
• A few traits are determined by a single
allele e.g. sex, blood group, inherited
diseases.
• Mutations - caused by miscopying of the
DNA of gametes resulting in changes in (or
loss of) proteins.
Environmental Variation
• Most variables are affected by the
environment.
• Skin colour, weight, height, dialects,
accents etc. are all influenced by this.
Most phenotypes are influenced by a
combination of genes and the
environment.
Examples
List 5 examples each of variation caused by:
– Genetics
– Environmental causes
– Both genetics and the environment
Collect data on the shoe size, eye colour, height
and handspan of at least 15 students. Find the
mean, median and mode where possible for
each set of data.
Mass Transport Surprise Test Review
• Look at the marks you got on each question.
• If your total is 14 or higher, you have passed (with
no revision!) – well done!
• Remember that all work you do from NOW will
build on this score.
• What do you need to do to improve?
HINT 1: Revise.
HINT 2: Review/consolidate your work each week.
HINT 3: Ask for help.
Homework
• Find the mark schemes to the questions on
the test.
• Annotate your test answers.
• Ask for help if you don’t understand
something.
• Have your annotated test ready to show me
next Friday (6th Feb).
Examples
List 5 examples each of variation caused by:
– Genetics
– Environmental causes
– Both genetics and the environment
Collect data on the shoe size, eye colour, height
and handspan of at least 15 students. Find the
mean, median and mode where possible for
each set of data.
Types of Variation - Continuous
• The full range of variables between 2 extreme
values.
• Examples in nature include : height, weight,
length, size.
• Data is normally presented as a line graph and
forms a normal distribution (a bell-shaped
curve).
Types of Variation - Discontinuous
• Also known as discrete variables.
• Variables are assigned to clearly defined
categories or distinct groups.
• Examples include : sex, blood groups, colour
• Data usually presented as a bar graph.
Appropriate Analysis
– Standard Deviation
A measure of spread about the mean.
Around 95% of values lie within 2 standard
deviations of the mean.
Appropriate Analysis
– Standard Deviation
s = standard deviation (sometimes written as 𝜎)
Σ = sum of (sigma)
x = measured value (from the sample)
𝑥 = mean value (x bar)
n = total number of values in the sample
Appropriate Analysis
– Standard Deviation
• Could be asked to calculate
it in the EMPA.
• For the exam, never asked
to calculate but could be
asked to interpret.
• Can use pen and paper or a
calculator.
Example:
Calculate the standard deviation of the following
numbers:
1, 3, 4, 6, 7, 8, 10, 12, 15, 20
Step 1 – calculate the mean
Step 2 – calculate (x - 𝒙) for each number…
Mean = 𝑥 = 8.6
x
𝑥
(x - 𝒙)
1
3
4
6
7
8
10
12
15
20
8.6
8.6
8.6
8.6
8.6
8.6
8.6
8.6
8.6
8.6
-7.6
-5.6
-4.6
-2.6
-1.6
-0.6
1.4
3.4
6.4
11.4
x
𝑥 (x - 𝒙) (x - 𝒙)2
1
8.6
3
8.6
4
8.6
6
8.6
7
8.6
8
8.6
10
8.6
12
8.6
15
8.6
20
8.6
-7.6
-5.6
-4.6
-2.6
-1.6
-0.6
1.4
3.4
6.4
11.4
57.76
31.36
21.16
6.76
2.56
0.36
1.96
11.56
40.96
129.96
Σ (x - 𝒙)2 = 304.4
= 33.822
= 5.816