Select the correct answer.

In a particular species of frogs, black spots are a dominant trait and their absence is a recessive trait. In a population of frogs, 50 are homozygous for the dominant trait, 34 are heterozygous dominant, and 16 show the recessive trait. Which expression is the correct way to calculate the frequency of the dominant allele?

A. [tex]\frac{50}{100}[/tex]

B. [tex]\frac{84}{100}[/tex]

C. [tex]\frac{50}{200}[/tex]

D. [tex]\frac{134}{200}[/tex]

E. [tex]\frac{100}{200}[/tex]



Answer :

To determine the frequency of the dominant allele in this population, we follow these steps:

1. Understanding Allele Frequency:
- The frequency of an allele in a population can be determined by counting the total number of that allele and then dividing by the total number of all alleles for the trait.

2. Identifying Genotypes:
- Homozygous dominant individuals (let's denote them as [tex]\(AA\)[/tex]) have two dominant alleles.
- Heterozygous dominant individuals (denoted as [tex]\(Aa\)[/tex]) have one dominant allele and one recessive allele.
- Recessive individuals (denoted as [tex]\(aa\)[/tex]) have two recessive alleles.

3. Counting Dominant Alleles:
- Each of the 50 homozygous dominant frogs contributes 2 dominant alleles. Therefore, the number of dominant alleles from homozygous dominant individuals is [tex]\(50 \times 2 = 100\)[/tex].
- Each of the 34 heterozygous frogs contributes 1 dominant allele. Therefore, the number of dominant alleles from heterozygous individuals is [tex]\(34 \times 1 = 34\)[/tex].

Combining these, the total number of dominant alleles is:
[tex]\[ 100 + 34 = 134 \][/tex]

4. Counting Total Alleles:
- Each frog, regardless of genotype, contributes 2 alleles (one from each parent). With 100 frogs in total (50 homozygous dominant + 34 heterozygous + 16 recessive), the total number of alleles is:
[tex]\[ 100 \times 2 = 200 \][/tex]

5. Calculating the Frequency of the Dominant Allele:
- The frequency of the dominant allele is the ratio of the number of dominant alleles to the total number of alleles. This is expressed as:
[tex]\[ \frac{\text{Number of dominant alleles}}{\text{Total number of alleles}} = \frac{134}{200} \][/tex]

Therefore, the correct answer is:
D. [tex]\(\frac{134}{200}\)[/tex]