If the frequency of a recessive phenotype in a stable population is 25%, the frequency of the dominant allelle in that popualation is:

Options

A. 0.5
B. 0.75
C. 0.25
D. 0.1

Answer

To find the frequency of the dominant allele in a stable population where the frequency of a recessive phenotype is 25%, we can follow these steps:

### Step 1: Understand the given information
The frequency of the recessive phenotype (which is represented by the genotype "aa") is given as 25%. This means that 25% of the population exhibits the recessive trait.

### Step 2: Use the Hardy-Weinberg principle
According to the Hardy-Weinberg principle, the frequency of genotypes in a population can be represented as:
- \( p^2 \) = frequency of homozygous dominant (AA)
- \( 2pq \) = frequency of heterozygous (Aa)
- \( q^2 \) = frequency of homozygous recessive (aa)

Where:
- \( p \) = frequency of the dominant allele (A)
- \( q \) = frequency of the recessive allele (a)

### Step 3: Calculate \( q \)
Since the frequency of the recessive phenotype (aa) is 25%, we can express this as:
\[ q^2 = 0.25 \]

To find \( q \), we take the square root of \( q^2 \):
\[ q = \sqrt{0.25} = 0.5 \]

### Step 4: Calculate \( p \)
Using the relationship \( p + q = 1 \), we can find \( p \):
\[ p + 0.5 = 1 \]
\[ p = 1 - 0.5 = 0.5 \]

### Step 5: Conclusion
The frequency of the dominant allele (A) in the population is:
\[ p = 0.5 \]

### Final Answer
The frequency of the dominant allele in that population is **0.5**.

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