Variation
Variation
- Variation means the differences between individuals.
- It can come from your genes, your environment, or both.
- And it falls into two patterns.
Three causes
- genetic only — set by the alleles you inherit (e.g. blood group).
- environmental only — set by your surroundings (e.g. a scar, the language you speak).
- both — most features (e.g. height, body mass) depend on genes and diet/lifestyle.
Practice
Most features, such as height, are caused by:
Height depends on the alleles inherited and on diet/lifestyle — a combination of genes and environment.
Two patterns
- discontinuous variation — clear, separate groups with nothing in between (e.g. blood group A/B/AB/O). Controlled by one or a few genes.
- continuous variation — a smooth range from one extreme to the other (e.g. height). Controlled by many genes plus the environment.
Practice
Continuous variation is:
Continuous variation (e.g. height) is a smooth range from many genes; discontinuous is separate groups from few genes.
Practice
Which is an example of discontinuous variation?
Blood group falls into clear separate categories — discontinuous variation.
The t-test
- To compare the means of two samples (e.g. plant heights in sun vs shade), use the t-test.
- It tells you whether the difference is large enough to be real, or just due to chance.
Practice
The t-test is used to:
The t-test checks whether the difference between two sample means is real or just chance.
You've got it
Key idea
- variation causes: genetic, environmental, or both
- discontinuous = separate groups (few genes); continuous = smooth range (many genes + environment)
- e.g. blood group = discontinuous; height = continuous
- the t-test compares two means — real difference or chance?