Free Continuous and Discontinuous Variation OCR A Level Biology revision notes – covering specification point 6.1.2(d).
Characteristics can demonstrate either continuous or discontinuous variation:
- Continuous variation is when individual characteristics range across many intermediate phenotype values, with no natural divisions.
- Discontinuous variation is when individual characteristics can be organised into separate, non-overlapping phenotypes, with no intermediates.
Continuous and discontinuous variation is determined by how many gene loci control a characteristic’s phenotype.
Continuous Variation
Characteristics that show continuous variation are typically polygenic, with many alleles each contributing a small amount to the phenotype through an additive effect.
The greater the number of gene loci involved, the wider range of phenotypes produced
The diagram below shows the distribution of adult height in a sample population, as an example of continuous variation:
Discontinuous Variation
Characteristics that show discontinuous variation are typically monogenic, with alleles having a large or all-or-nothing effect on the phenotype.
The diagram below shows the distribution of ABO blood group in a sample population, as an example of discontinuous variation:
