To determine the frequency of the recessive allele in the population of chickens, we need to follow these detailed steps:
1. Identify the given information:
- Homozygous dominant (RR): 45 chickens
- Heterozygous dominant (Rr): 30 chickens
- Homozygous recessive (rr): 25 chickens
2. Calculate the total number of chickens:
[tex]\[
\text{Total chickens} = 45 + 30 + 25 = 100
\][/tex]
3. Determine the number of recessive alleles:
- Homozygous recessive (rr) chickens contribute 2 recessive alleles each.
- Heterozygous dominant (Rr) chickens contribute 1 recessive allele each.
Therefore:
[tex]\[
\text{Recessive alleles from rr chickens} = 25 \times 2 = 50
\][/tex]
[tex]\[
\text{Recessive alleles from Rr chickens} = 30 \times 1 = 30
\][/tex]
Adding these together gives the total number of recessive alleles:
[tex]\[
\text{Total recessive alleles} = 50 + 30 = 80
\][/tex]
4. Calculate the total number of alleles in the population:
Since each chicken has 2 alleles:
[tex]\[
\text{Total number of alleles} = 100 \times 2 = 200
\][/tex]
5. Calculate the frequency of the recessive allele:
The frequency of the recessive allele is the proportion of recessive alleles out of the total number of alleles:
[tex]\[
\text{Frequency of recessive allele} = \frac{80}{200}
\][/tex]
So, the correct way to calculate the frequency of the recessive allele is:
[tex]\[
\boxed{\frac{80}{200}}
\][/tex]
The correct answer is B.
