A population will not exist in Hardy-Weinberg equilibrium if:

Options

A. There is no migration
B. The population is large
C. Individuals mate selectively
D. There are no mutations

Answer

### Step-by-Step Solution:

1. **Understanding Hardy-Weinberg Equilibrium**:
- The Hardy-Weinberg equilibrium is a principle that describes a population that is not evolving. For a population to be in this state, certain conditions must be met, including no mutations, random mating, no natural selection, extremely large population size, and no gene flow (migration).

2. **Identifying Factors that Disrupt Equilibrium**:
- Any factor that introduces changes to the allele frequencies in a population can disrupt the Hardy-Weinberg equilibrium. The main factors include:
- **Mutations**: Changes in the DNA sequence can introduce new alleles into the population.
- **Genetic Drift**: Random changes in allele frequencies, particularly in small populations.
- **Migration (Gene Flow)**: Movement of individuals into or out of a population can alter allele frequencies.
- **Natural Selection**: Differential survival and reproduction can lead to changes in allele frequencies.
- **Non-random Mating**: If individuals preferentially mate based on certain traits, it can affect allele frequencies.

3. **Analyzing the Given Options**:
- The question asks which condition would prevent a population from being in Hardy-Weinberg equilibrium. We need to evaluate the options based on the criteria established.
- **Option 1: No migration** - This is a condition for Hardy-Weinberg equilibrium; thus, this option does not disrupt it.
- **Option 2: Population is large** - A large population size helps maintain equilibrium; therefore, this option does not disrupt it.
- **Option 3: Individuals mate selectively** - This introduces non-random mating, which can lead to changes in allele frequencies and disrupt equilibrium.
- **Option 4: No mutation** - This is also a condition for maintaining Hardy-Weinberg equilibrium; thus, this option does not disrupt it.

4. **Conclusion**:
- The correct answer is that a population will not exist in Hardy-Weinberg equilibrium if **individuals mate selectively** (Option 3).