1. What is Selection Coefficient?

Definition: The selection coefficient (s) measures the relative fitness difference between a new variant and the original form in a population.

Purpose: It quantifies the strength of natural selection acting on genetic variants or traits in evolutionary biology and population genetics.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( s \) — Selection coefficient (dimensionless)
• \( f_{new} \) — Fitness of new variant (context-specific)
• \( f_{old} \) — Fitness of original variant (context-specific)

Explanation: The difference in fitness between new and old variants is divided by the old fitness to get the relative strength of selection.

3. Interpretation of Selection Coefficient

Details:

• s > 0: New variant is favored by selection
• s = 0: No selection difference
• s < 0: New variant is selected against

4. Using the Calculator

Tips: Enter the fitness values for both variants. The old fitness must be greater than zero. Fitness can be measured as survival rate, reproductive success, or other relevant metrics.

5. Frequently Asked Questions (FAQ)

Q1: What units are used for fitness values?
A: Fitness is typically unitless, representing relative reproductive success (often scaled to 1 for the reference variant).

Q2: What's considered a strong selection coefficient?
A: In evolutionary biology, |s| > 0.01 is typically considered significant, with |s| > 0.1 being strong selection.

Q3: Can the selection coefficient be greater than 1?
A: Yes, if the new variant has more than double the fitness of the old variant (f_new > 2×f_old).

Q4: How is this different from relative fitness?
A: The selection coefficient is essentially relative fitness minus 1 (s = w - 1 where w is relative fitness).

Q5: What does a negative selection coefficient mean?
A: It indicates the new variant is less fit than the original and will be selected against.