Directional selection increases the frequency of individuals expressing one of the extreme phenotypic traits in a population. Otion A). Directional selection is working here.
What is Directional Selection?
Directional selection is one of the different types of natural selection.
It increases in the proportion of individuals with an extreme phenotypic trait.
It causes a decrease in the number of individuals expressing intermediate phenotype, and the other extreme phenotype.
This selection presents more frequently in those cases in which interactions between living organisms and the environment modify in the same direction.
In the exposed example,
There was an original wide range of salmon sizes.
One extreme phenotype is the largest fishes, and the other extreme phenotype is the smaller fishes.
The largest phenotype was the one affected by the fishing pressure.
The smallest fishes survived.
The alleles coding for the small size phenotype increased the species' fitness, so natural selection favored this extreme phenotype.
Small-sized fishes were favored over medium and large-sized fishes.
Directional selection is working here.
You will learn more about directional selection at
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