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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{5}{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, we need to consider the contribution of each genetic group (homozygous dominant, heterozygous dominant, and homozygous recessive) to the gene pool.

Here's a step-by-step breakdown:

1. Determine the total population:
- Homozygous dominant (AA): 45
- Heterozygous dominant (Aa): 30
- Homozygous recessive (aa): 25
- Total population = 45 (AA) + 30 (Aa) + 25 (aa) = 100

2. Count the total number of alleles in the population:
Each chicken has 2 alleles for the comb trait.
- Total alleles = Total population 2
- Total alleles = 100 2 = 200 alleles in the population

3. Count the total number of recessive alleles (a) present:
- Homozygous dominant (AA) individuals have 0 recessive alleles.
- Heterozygous dominant (Aa) individuals have 1 recessive allele each.
- Recessive alleles contributed by heterozygous dominant = 30 1 = 30
- Homozygous recessive (aa) individuals have 2 recessive alleles each.
- Recessive alleles contributed by homozygous recessive = 25 2 = 50
- Total recessive alleles = 30 (from Aa) + 50 (from aa) = 80

4. Calculate the frequency of the recessive allele (a):
The frequency of the recessive allele is the number of recessive alleles divided by the total number of alleles.
- Frequency of the recessive allele (a) = Total recessive alleles / Total alleles
- Frequency of the recessive allele = 80 / 200 = 0.4 or 40%

Thus, the correct expression to calculate the frequency of the recessive allele in the population is
[tex]\[ \frac{80}{200} \][/tex]

So, the correct answer is:
[tex]\[ \boxed{\text{B. } \frac{80}{200}} \][/tex]

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