# 99 Variation continuous and discontinous
Variation is all the differences which exist between members of the same species. It is caused by a combination of genetic and environmental factors. There are two kinds of variation: continuous and discontinuous.
Continuous variation
- shows a complete range of the characteristic within a population.
- caused both by both gens (often a number of different genes) and environment:
Discontinuous variation
- seen where there are obvious, distinct categories for a feature.
- no intermediates between categories, the feature cannot usually change during life.
- caused by a single gen/a small number of genes, with no environmental influence.
- shows a complete range of the characteristic within a population.
- caused both by both gens (often a number of different genes) and environment:
- Plants: availability of/competition for: nutrients, light, water;
- Animals: availability of food/balanced diet
Discontinuous variation
- seen where there are obvious, distinct categories for a feature.
- no intermediates between categories, the feature cannot usually change during life.
- caused by a single gen/a small number of genes, with no environmental influence.
Try this
Seventy seeds were collected from a cross between two plants of the same species. The seeds were sown at the same time and, after 3 weeks, the heights of the plants which grew were measured and found to fall in to two groups, A and B, as shown in figure below.
Seventy seeds were collected from a cross between two plants of the same species. The seeds were sown at the same time and, after 3 weeks, the heights of the plants which grew were measured and found to fall in to two groups, A and B, as shown in figure below.
a) Calculate the percentage of seeds which germinated. Show your working. [2 marks]
b) i) Name the type of variation shown within each group [1 mark]
ii) State three factors which might have caused this variation. [3 marks]
Answer
a) 56/70x100=80%
b) i) continuous variation.
ii) Any 3 factors from: genes, temperature, disease, seed size, light, O2, CO2, H2O, minerals, mutation, trampling by animals.
Video: What is meant by genetic difference?
b) i) Name the type of variation shown within each group [1 mark]
ii) State three factors which might have caused this variation. [3 marks]
Answer
a) 56/70x100=80%
b) i) continuous variation.
ii) Any 3 factors from: genes, temperature, disease, seed size, light, O2, CO2, H2O, minerals, mutation, trampling by animals.
Video: What is meant by genetic difference?