Which of the following is correct about Hardy Weinberg's principle ?

Options

A. `p^2` is the number of pure homozygous dominant individuals in the population , `q^2` is the number of pure homozygous recessive individuals in the population.
B. `p^2` is the number of pure homozygous dominant recessive individuals in the population , `q^2` is the number of pure homozygous dominant individuals in the population and 2pq is the number of heterozygous individuals in the population.
C. `p^2` is the proportion of pure homozygous dominant individuals in the population , `q^2` is the proportion of pure homozygous recessive individuals in the population and 2pq is the proportion of heterozygous individuals in the population.
D. `p^2` is the proportion of pure homozygous recessive individuals in the population , `q^2` is the proportion of pure homozygous dominant individuals in the population and 2pq is the proportion of heterozygous individuals in the population.

Answer

To solve the question regarding the Hardy-Weinberg principle, we need to analyze the statements provided in the options and determine which one correctly describes the principle.

### Step-by-Step Solution:

1. **Understanding the Hardy-Weinberg Principle**:
The Hardy-Weinberg principle provides a mathematical model to study genetic variation in a population. It states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences.

2. **The Hardy-Weinberg Equation**:
The equation is represented as:
\[ p^2 + 2pq + q^2 = 1 \]
where:
- \( p^2 \) = frequency of homozygous dominant individuals (AA)
- \( 2pq \) = frequency of heterozygous individuals (Aa)
- \( q^2 \) = frequency of homozygous recessive individuals (aa)

3. **Analyzing Each Option**:
- **Option 1**: States that \( p^2 \) is the number of pure homozygous dominant individuals and \( q^2 \) is the number of pure homozygous recessive individuals, but it does not mention \( 2pq \). This option is incorrect.
- **Option 2**: Claims \( p^2 \) is the number of pure homozygous dominant recessive individuals, which is a contradiction, and also misstates \( q^2 \). This option is incorrect.
- **Option 3**: Correctly states that \( p^2 \) is the proportion of pure homozygous dominant individuals, \( q^2 \) is the proportion of pure homozygous recessive individuals, and \( 2pq \) is the proportion of heterozygous individuals. This option is correct.
- **Option 4**: Incorrectly states that \( p^2 \) is the proportion of pure homozygous recessive individuals and \( q^2 \) is the proportion of pure homozygous dominant individuals. This option is incorrect.

4. **Conclusion**:
The correct statement about the Hardy-Weinberg principle is found in **Option 3**.

### Final Answer:
**Option 3 is correct.**