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Variation
Variation is simply the differences we see between individuals of the same species. These differences can be due to the unique genetic information inherited from parents, how genes are shuffled during reproduction, or even the environment we grow up in.
Need to know
What you need to know
- **Genetic Variation**: These are inherited differences in an organism's DNA sequence, passed down from parents to offspring. They are determined by the specific **alleles** (different forms of a gene) an individual possesses. Examples include human blood groups (A, B, AB, O) and natural eye colour (though environmental factors can influence pigment *expression* slightly, the underlying genetic blueprint is fixed).
- **Environmental Variation**: These differences arise from the influence of external factors on an organism during its lifetime. They are not inherited. Examples include a person's tan (due to sun exposure), muscle development (due to exercise), or the exact height a plant reaches (influenced by nutrient availability, light, and water).
- Many characteristics, such as human height or intelligence, are influenced by *both* genetic predisposition and environmental factors. The genotype sets the potential range, while the environment determines where within that range the phenotype is expressed.
Explanation
Why are we all different?
- Distinguish clearly between genetic and environmental causes of variation.
- Know the characteristics and examples of continuous vs. discontinuous variation.
- Understand the specific mechanisms in meiosis (crossing over, independent assortment) and fertilisation that create genetic diversity.
- Practise explaining how variation gives a species an evolutionary advantage.