Question:
Two bacterial variants are growing together in the same flask. At any relative frequency of the two variants, the population growth rate of the rarer variant is higher. This is an example of ________.
Two bacterial variants are growing together in the same flask. At any relative frequency of the two variants, the population growth rate of the rarer variant is higher. This is an example of ________.
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Fitness of the rarer type being higher, no matter the frequency, is the definition of negative frequency-dependent selection.
Updated On: Jul 20, 2026
- sexual selection
- positive selection
- negative frequency-dependent selection
- positive frequency-dependent selection
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The Correct Option is C
Solution and Explanation
Step 1: Identify the pattern described.
The question says that whichever variant is currently rarer grows faster, no matter what the actual frequencies are. So fitness (growth rate) depends on how common a type is, and it depends in a way that favors the minority.
Step 2: Recall frequency-dependent selection.
Frequency-dependent selection is any situation where the fitness of a type changes with its own frequency in the population. There are two directions this can go.
Step 3: Define negative frequency-dependent selection.
In negative frequency-dependent selection, a type's fitness rises as it becomes rarer and falls as it becomes more common. This tends to keep both types in the population together, because whichever type starts losing ground gets a fitness boost that pulls it back up. This matches the flask scenario exactly.
Step 4: Define positive frequency-dependent selection for contrast.
In positive frequency-dependent selection, a type's fitness rises as it becomes more common, which pushes the population toward having only the common type and drives the rare type to extinction. This is the opposite of what is described here.
Step 5: Rule out the remaining options.
Sexual selection concerns fitness differences from competition for mates or mate choice, not simple abundance. Positive selection is a general term for selection favoring a particular allele or trait outright, again with no mention of frequency dependence. Neither fits the rarer-type-wins pattern in the question.
Step 6: Conclude.
\[ \boxed{\text{Negative frequency-dependent selection}} \]
The question says that whichever variant is currently rarer grows faster, no matter what the actual frequencies are. So fitness (growth rate) depends on how common a type is, and it depends in a way that favors the minority.
Step 2: Recall frequency-dependent selection.
Frequency-dependent selection is any situation where the fitness of a type changes with its own frequency in the population. There are two directions this can go.
Step 3: Define negative frequency-dependent selection.
In negative frequency-dependent selection, a type's fitness rises as it becomes rarer and falls as it becomes more common. This tends to keep both types in the population together, because whichever type starts losing ground gets a fitness boost that pulls it back up. This matches the flask scenario exactly.
Step 4: Define positive frequency-dependent selection for contrast.
In positive frequency-dependent selection, a type's fitness rises as it becomes more common, which pushes the population toward having only the common type and drives the rare type to extinction. This is the opposite of what is described here.
Step 5: Rule out the remaining options.
Sexual selection concerns fitness differences from competition for mates or mate choice, not simple abundance. Positive selection is a general term for selection favoring a particular allele or trait outright, again with no mention of frequency dependence. Neither fits the rarer-type-wins pattern in the question.
Step 6: Conclude.
\[ \boxed{\text{Negative frequency-dependent selection}} \]
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