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In chickens, a flat single comb is a recessive trait, while the short, thick rose comb is dominant. In a particular population of chickens, 45 are homozygous for the dominant trait, 30 are heterozygous dominant, and 25 have the recessive trait. Which expression is the correct way to calculate the frequency of the recessive allele?

A. [tex]$\frac{90}{100}$[/tex]
B. [tex]$\frac{80}{200}$[/tex]
C. [tex]$\frac{55}{100}$[/tex]
D. [tex]$\frac{55}{200}$[/tex]
E. [tex]$\frac{120}{200}$[/tex]



Answer :

GinnyAnswer
To determine the frequency of the recessive allele in a population of chickens with given genotypes, let's follow the steps below:

1. Count the number of individuals with each genotype:
- Homozygous dominant (RR): 45 chickens
- Heterozygous dominant (Rr): 30 chickens
- Recessive trait (rr): 25 chickens

2. Calculate the total number of chickens:
[tex]\[ \text{Total chickens} = 45 + 30 + 25 = 100 \][/tex]

3. Determine the number of dominant alleles:
- Each homozygous dominant (RR) chicken contributes 2 dominant alleles:
[tex]\[ 45 \times 2 = 90 \quad (\text{alleles}) \][/tex]
- Each heterozygous dominant (Rr) chicken contributes 1 dominant allele:
[tex]\[ 30 \times 1 = 30 \quad (\text{alleles}) \][/tex]
[tex]\[ \text{Total dominant alleles} = 90 + 30 = 120 \][/tex]

4. Determine the total number of alleles in the population:
- Since each chicken has 2 alleles, the total number of alleles is:
[tex]\[ 100 \times 2 = 200 \][/tex]

5. Calculate the number of recessive alleles:
- The number of recessive alleles is the total number of alleles minus the number of dominant alleles:
[tex]\[ \text{Recessive alleles} = 200 - 120 = 80 \][/tex]

6. Calculate the frequency of the recessive allele:
- The frequency is the number of recessive alleles divided by the total number of alleles:
[tex]\[ \text{Frequency of recessive allele} = \frac{80}{200} = 0.4 \][/tex]

Given the steps above, the correct expression for calculating the frequency of the recessive allele is:

B. [tex]\(\frac{80}{200}\)[/tex]

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