Worked example 1
Explain how both genetic and environmental factors contribute to the variation in human height, and discuss why genetic variation is crucial for the long-term survival of a species. [8 marks]
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- Genetic Factors for Height: Human height is a polygenic trait, meaning it's controlled by multiple genes, each often having several alleles. The specific combination of these alleles inherited from parents determines an individual's genetic potential or predisposition for height. Different alleles contribute small, additive effects to height, leading to the continuous range observed in human populations.
- Environmental Factors for Height: While genetics sets the potential, environmental factors significantly influence the expression of this potential. Key environmental influences include nutrition (e.g., sufficient intake of protein, vitamins, and minerals, especially during critical growth periods like childhood and adolescence), health (e.g., absence of chronic diseases, infections, or hormonal imbalances), and access to healthcare. Poor nutrition or persistent illness can prevent an individual from reaching their full genetic potential for height.
- Cruciality of Genetic Variation for Species Survival: Genetic variation provides the raw material upon which natural selection acts. In a population with diverse alleles, some individuals will possess traits (phenotypes) that are better suited or advantageous in a particular environment.
- If environmental conditions change (e.g., emergence of a new pathogen, climate shift, habitat alteration), individuals with pre-existing advantageous alleles are more likely to survive, reproduce, and pass on these beneficial traits to their offspring.
- This differential survival and reproduction lead to a shift in allele frequencies within the population over generations, resulting in adaptation and evolution. Without genetic variation, a species would lack the ability to adapt to changing environments, making it highly vulnerable to extinction, thereby ensuring its long-term survival in dynamic ecosystems.