Lesson 6 - Representing Variation Flashcards
How is variation studied?
- Scientists take measurements of different characteristics within a species.
- Collect measurements from large numbers of the population to ensure that reliable conclusions are formed.
- Represent the data graphically, this enables patterns to be seen.
Different types of variation shown by data collected?
- Discontinuous variation
- Continuous variation
Discontinuous variation?
Characteristic that can only result in certain values is said to show discontinuous variation.
Continuous variation?
Two extremes with a full range of values in-between. There is a graduation in values from one extreme to the other of a characteristic (this is known as continuum)
Examples of continuous variation?
- Height
- Weight
- Number of antigens on a cell
- Number of leaves on a tree
Draw a graph for continuous variation?
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What traits show continuous variation?
Those regulated by multiple genes (polygenes) and influenced by the environment
Discontinuous variation definition?
Distinct categories with no intermediate values.
Examples of discontinuous data?
- Hair colour
- Animals sex
- Blood group
- Shape of bacteria
- Spherical (cocci)
- Rods (bacilli)
- Spiral (spirilla)
- Comma (vibrios)
- Corkscrew shaped (spirochaetes)
Distribution of discontinuous data?
Individuals tend to be distributed evenly between different categories.
What factors are traits that show discontinuous data influenced by?
Regulated by a single gene and aren’t under environmental influence.
Representation of discontinuous data?
- Bar chart
- Pie chart
What single gene are blood groups controlled by?
ABO gene
Data representation of continuous variation?
- Frequency table
- Plotted onto histogram
- Curve is drawn on graph to show trend.
What is a normal distribution curve?
Bell shaped curve which usually represents the distribution of continuous data.
Characteristics of a normal distribution curve?
- Mean, mode and median are the same
- Distribution has a characteristic ‘bell shape’ which is symmetrical about the mean.
- 50% of values are less than the mean and 50% are greater than the mean.
- Most values lie close to the mean value - the number of individuals at extreme are low.
Standard deviation?
- Measure of how spread out the data is.
- The greater the standard deviation, the greater the spread of data.
- In variation, a characteristic with a high standard deviation has a large amount of variation.
Usual findings of standard deviation:
- 68% of values are within 1 standard deviation of the mean
- 95% of values are within 2 standard deviations of the mean
- 99.7% of values are within 3 standard deviations of the mean.
Equation for standard deviation?
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Flagella length variation in salmonella?
Salmonella bacteria have a number of flagella to enable them to move. There is continuous variation within the length of the salmonella flagella.
Student’s t test
Compare the means of data values from two populations.
- Data collected must be normally distributed and enough data should be collected to calculate a reliable mean. Different sample sizes may be used.
Spearman’s rank correlation coefficient?
Used to consider the relationship between two sets of data.
If two sets of data are related they are said to be correlated.
Spearmen’s rank correlation coefficient?
Types of data shown?
- No correlation (no relationship between the data)
- Positive correlation (as one set of data increases in value, the other set of data also increases in value)
- Negative correlation (as one set of data increases in value, the other set of data decreases in value)
