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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{50}{200}[/tex]
D. [tex]\frac{85}{200}[/tex]
E. [tex]\frac{120}{200}[/tex]



Answer :

GinnyAnswer
To determine the frequency of the recessive allele in the given chicken population, we follow these steps:

1. Identify the total number of chickens:
- Homoyzgous dominant (RR): 45
- Heterozygous dominant (Rr): 30
- Recessive (rr): 25

Therefore, the total number of chickens is:
[tex]\[ 45 + 30 + 25 = 100 \][/tex]

2. Calculate the total number of alleles:
Each chicken has 2 alleles. So, the total number of alleles in the population is:
[tex]\[ 100 \times 2 = 200 \][/tex]

3. Determine the number of recessive alleles:
- Homoyzgous dominant (RR) chickens contribute 0 recessive alleles.
- Heterozygous dominant (Rr) chickens contribute 1 recessive allele each.
- Recessive (rr) chickens contribute 2 recessive alleles each.

Therefore, the total number of recessive alleles is:
[tex]\[ 0 \times 45 + 1 \times 30 + 2 \times 25 = 0 + 30 + 50 = 80 \][/tex]

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

Therefore, the correct expression to calculate the frequency of the recessive allele is:
[tex]\[ \boxed{B.\ \frac{80}{200}} \][/tex]

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