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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]$\frac{80}{100}$[/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 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.

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