Causes of variationSpec 3.20
Differences between individuals of the same species are called variation. Variation in phenotype has two causes: genes and the environment. Often it is a combination of both.
| Genetic variation | Environmental variation | |
|---|---|---|
| What it is | Different characteristics as a result of mutation and sexual reproduction | Different characteristics caused by an organism's environment (acquired characteristics) |
| Source | Differences in the alleles inherited | Conditions during life, such as diet, climate, injury or activity |
| Examples | Eye colour, sex | A scar, body mass affected by diet, plant height affected by light |
Continuous and discontinuous variation
- Continuous variation: the feature can take any value in a range, such as height or mass. The results are shown on a histogram.
- Discontinuous variation: the feature falls into distinct categories with nothing in between, such as sex or purple versus white flowers. The results are shown on a bar chart.
Calculating an arithmetic mean
The heights of five seedlings grown in the same conditions were 12 cm, 15 cm, 11 cm, 14 cm and 13 cm. Calculate the mean height.
- Add the values: 12 + 15 + 11 + 14 + 13 = 65 cm.
- Divide by the number of values: 65 ÷ 5 = 13 cm.
Answer: Mean height = 13 cm.