What is variation?

Differences that exists between individuals

What is intraspecific variation?

Variation between members of a species

What is interspecific variation?

Variation between species

Name 2 causes of variation

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- Genetic factors
- Environment

Differences in environment cause variation _____ species

within

Describe how genetic factors cause variation between species

Different species have different genes = variation between species

Describe how genetic factors cause variation within species

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- Individuals of same species have same genes but different alleles
- Polygenes - lots of genes can control one feature

What is most variation within species caused by?

A combination of genetic and environmental factors

Give an example of how both genetic and environmental factors can cause variation

e.g. genes determine how tall organism can grow but nutrient availability affects how tall organism actually grows

Samples are used as ____ for a whole population

models

Why does a sample has to be random?

∵ it's used to draw conclusions about a whole population ∴ has to accurately represent the whole population

How do you make sure a sample isn't biased?

By making sure it's random

Describe how you would carry out random sampling

e.g.

- Divide field into grid and use random number generator to select coordinates
- Take samples at the intersection of each pair of coordinates

Name 2 ways to minimise the variation observed in a sample occuring due to chance

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- Analysing data statistically
- Using a large sample size

How will analysing data statistically minimise the variation observed in sample occuring due to chance?

Allows us to decide whether variation observed is due to chance or some other cause

How will using a large sample size minimise the variation observed in sample occuring due to chance?

More individuals selected = smaller the probability that chance will influence the result

What can the mean used be for when measuring variation?

Can be used to look for variation **between** samples

What type of graph do most samples (of continuous variation) result in and why?

Bell-shaped graph, AKA normal distribution, ∵ most samples will include values either side of mean

Sketch a normal distribution curve & label where the mean would be

Measuring Variation

What does the standard deviation tell you?

Tells you about variation **within** a sample i.e. how much values in a single sample vary

What is standard deviation?

Measure of the spread of values about the mean

What does a large standard deviation mean?

Values in sample vary a lot

What does a small standard deviation mean?

Most of sample is around mean value = varies little

In normal distribution curve, how is the standard deviation represent?

By the width of the curve

What is meant by 9 ± 3?

Means that mean = 9 & that the standard deviation = 3 so most of the vaules are spread between 6-12

Standard deviations can be plotted on a graph/chart of mean values using ____ _____

error bars

Error bars extend one...

standard deviation above and one standard deviation below the mean

The longer the error bar...

the larger the standard deviation & more spread sample data is from mean

When comparing variation in size between 2 groups of organisms, it is often considered more useful to compare standard deviations rather than ranges. Explain why. (2)

So that anomalies of either very short or very long don't skew the results

What is discontinuous variation caused by?

Due to genetic factors (& organisms fit into few distinct groups)