Directional selection is a mode of natural selection where one extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that favored phenotype. In simpler terms, if a population has a range of traits, and one particular trait helps individuals survive and reproduce better in their environment, that trait will become more common in future generations. This leads to a shift in the population's characteristics over time.
Imagine a population of birds with beaks of different sizes. If the only available food source is deep inside long, narrow flowers, birds with longer beaks will be more successful at obtaining food. As a result, they will have more offspring, and the proportion of birds with longer beaks will increase in the population over generations.
Match the following terms with their definitions:
| Term | Definition |
|---|---|
| 1. Phenotype | A. The process where allele frequencies shift over time. |
| 2. Allele Frequency | B. The genetic makeup of an organism. |
| 3. Natural Selection | C. The observable characteristics of an organism. |
| 4. Genotype | D. The proportion of a specific allele in a population. |
| 5. Directional Selection | E. A type of selection that favors one extreme phenotype. |
Match the term to the definition:
Complete the following paragraph with the correct words:
__________ selection occurs when one __________ trait is favored, causing a shift in the __________ frequency. This process leads to an increase in the proportion of individuals with the __________ phenotype, enhancing their __________ and reproductive success.
Provide a detailed answer to the following question:
Give an example (different from the bird beak example) of directional selection in a real-world population. Explain the environmental pressure, the trait being selected, and the expected outcome over time.
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