Environmental variation refers to differences caused by the conditions in which an organism lives and grows. These are often called 'acquired characteristics' because they are not coded in the DNA at birth.
Factors such as climate, diet, and lifestyle play a significant role in shaping an individual. For instance, a plant grown in low light may become taller and thinner as it stretches toward a light source, a process driven by its surroundings.
Physical changes resulting from accidents, such as scarring, or cultural influences, such as the language or accent a person speaks, are purely environmental and cannot be passed on to offspring through genes.
Many characteristics are the result of a combination of both genetic and environmental causes. While genes provide the 'potential' for a trait, the environment determines the extent to which that potential is realized.
Height is a classic example of this interaction. An individual may inherit genes for being tall from their parents, but if their diet is poor during development, they may not reach their full genetic height potential.
This relationship can be summarized by the idea that genes decide the possible range of characteristics we can inherit, while the surrounding environment affects how those inherited characteristics actually develop.
All genetic variants originally arise from mutations, which are random changes in the DNA sequence. These changes occur continuously and spontaneously within a population.
Most mutations have no effect on the phenotype because the resulting protein functions the same way as the original. However, a small number of mutations can lead to new alleles and distinct new phenotypes.
In rare cases, a mutation may provide a survival advantage. If a new phenotype is better suited to an environmental change, such as a change in camouflage color, it can lead to rapid shifts in the characteristics of the population.
| Feature | Genetic Variation | Environmental Variation |
|---|---|---|
| Primary Cause | DNA inheritance and mutations | Surroundings, diet, and lifestyle |
| Inheritability | Can be passed to offspring | Cannot be passed to offspring |
| Stability | Fixed from birth | Can change throughout life |
| Examples | Blood type, eye color | Scars, language, tan |
Identify the Cause: When asked to categorize a trait, ask yourself: 'Can this trait be changed by the way the organism lives?' If yes, it has an environmental component. If it is fixed from birth (like blood type), it is purely genetic.
The Mutation Rule: Always remember that mutations are the ultimate source of all genetic variation. If a question asks where a brand-new trait came from in a population, the answer is almost always a random mutation.
Check for Interaction: Be careful with traits like weight or height. Examiners often use these to test your understanding of how genes and environment work together. Never assume a complex physical trait is 100% genetic.
Terminology Precision: Use the term phenotype when discussing the outward appearance and genotype (or genetic makeup) when discussing the underlying DNA.
