A polymorphism is the occurrence of two or more clearly different phenotypes within the same population of a species - it reflects the effects of more than one allele in the gene pool
▪ A situation when there are two alleles in a gene pool (polymorphic) and one allele is gradually replacing another
This is due to a strong environmental selective pressure causing directional selection to eliminate one allele
The Peppered Moth is another example of evolution in response to environmental change. There are two types of these moths; one species has a light color while the other one is darker. When Britain begun industrializing, the soot from the factories would land on trees and so the darker moths then had an advantage over the light ones as they could easily hide from predators. Before the soot, both types of moths were eaten by predators however now that the darker ones were able to hide the lighter ones got eaten more often. The population of the darker moths rapidly increased while that of the lighter ones rapidly decreased until only the dark moths were left. All the lighter moths were less adapted to the environmental change and so they could no longer survive in that new environment.
Example 2: Peppered Moth (Biston betularia)
Variation: Colouration (some moth have a light colour, while others are a darker melanic colour)
Environmental change: Pollution from industrial activities caused trees to blacken with soot during the Industrial Revolution
Response: Light coloured moths died from predation, whereas melanic moths were camouflaged and survived to pass on their genes
Evolution: Over time, the frequency of the melanic form increased (with improved industrial practices, the lighter variant has become more common)
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