By the end of this lesson
- Distinguish genetic and environmental variation.
- Classify continuous and discontinuous variation.
- Explain genotype–environment interaction.
BIG QUESTION
Why do individuals in one species differ even when they share a habitat?
Inherited alleles and life experiences both contribute to phenotype.
Genetic variation is inherited
Mutations create new alleles; meiosis and fertilisation create new combinations. These differences can be passed to offspring when present in gametes.
Blood group is largely genetically determined and shows discontinuous categories.
Environment also changes phenotype
Diet, disease, exercise, education and habitat can affect characteristics without necessarily changing DNA sequence. Sun exposure can alter skin pigmentation temporarily.
Environmental effects may be reversible or irreversible depending on timing and mechanism.
Most characteristics involve interaction
Height is influenced by many genes and by nutrition and health. A genotype can set a range of possible outcomes while environment influences where an individual develops within it.
Continuous variationDifferences between individuals of the same species, caused by genes, the environment or both. has many intermediate values; discontinuous variationVariation in which a feature falls into distinct categories with no values in between, such as blood group. has distinct categories.
Sources and patterns of variation
Classify both cause and distribution.
| Type | Cause | Example |
|---|---|---|
| Genetic | Alleles inherited from parents. | ABO blood group. |
| Environmental | Conditions/experiences. | Accent learned from community. |
| Both | Genotype × environment. | Height. |
| Continuous | Range of values. | Mass or height. |
| Discontinuous | Separate categories. | Blood group. |
Language that earns precision
- variation
- Differences between individuals in a population.
- continuous variation
- Variation across a range with many intermediate values.
- discontinuous variation
- Variation in distinct categories with no intermediates.
- environmental variation
- Differences caused by conditions and experiences rather than inherited DNA sequence.
Common misconceptions
Claim: Every difference is inherited.
Correction: Some result from environmental conditions or choices.
Claim: Environmental variation changes genes automatically.
Correction: It can change phenotype without changing DNA sequence.
Claim: A continuous distribution proves only one cause.
Correction: It often reflects many genes and/or environmental factors.
Match the answer to the command word
Give both source of variation and a justified example.
Genes influence potential; environment influences outcome.
Recall, apply, then justify
Distinguish genetic and environmental variation using one example of each.
Hint
Inherited allele versus condition/experience.
Suggested marking points
- Genetic variation is caused by inherited allele/DNA differences.
- ABO blood group is an example of mainly genetic variation.
- Environmental variation is caused by conditions or experiences.
- A scar or sun tan is an example of environmental variation.
Explain why height is influenced by both genetic and environmental factors.
Hint
Polygenic potential and nutrition/health.
Suggested marking points
- Many genes influence growth potential.
- Nutrition, health and other environmental conditions affect the final height.
Design a study comparing genetic and environmental effects on a characteristic using twins.
Planning hint
Compare similarity and shared environment carefully.
What a strong design includes
- Compare identical and non-identical twin pairs.
- Measure the characteristic consistently.
- Record relevant shared and differing environments.
- Identical twins share more genetic similarity than non-identical twins.
- Greater similarity in identical twins can support a genetic contribution.
- Twin studies cannot fully separate genes from shared environment.
- Use consent, privacy and careful non-deterministic interpretation.