Q23.2-1CC(1) - Campbell Biology

Question

A population has 700 individuals, 85 of genotype AA, 320 of genotype Aa, and 295 of genotype aa. What are the frequencies of alleles A and a?

Step-by-Step Solution

Answer

The frequency of allele A is 0.35, and the frequency of allele a is 0.65. 

Step 1: Allele

The genetic factor that codes for a different version of a particular trait is called an allele. Alleles exist in alternative forms. Alleles occupy the corresponding position on the locus of the homologous chromosome. 

The alleles which control the same character might produce different phenotypical effects based on their numbers and dominancy. 

Step 2: Equation to find out allele frequency

The frequency of alleles equals the number of alleles in a population divided by the total number of alleles. Therefore, in the given problem, the total number of alleles in a population is 1400 because the number of alleles present in each individual is 2. So, $700\times 2=1400$

Step 3: Frequency of allele “A”

The A allele present in 295 individuals is ‘0’ because they do not have A alleles.

The 85 individuals have a genotype of AA; thus, they have two A alleles, and 320 individuals have Aa, so one A allele is present.

The frequency of allele A is,

$$\begin{gathered} p=\frac{2\times 85+1\times 320+0\times 295}{1400} \\ p=\frac{170+320}{1400} \\ p=\frac{490}{1400} \\ p=0.35 \end{gathered}$$

Hence, the frequency of the ‘A’ allele is 0.35 because ‘p’ stands for the frequency of ‘A’ allele. 

Step 4: Frequency of allele “a”

The number of ‘a’ alleles present in 85 individuals is 0; in 295 individuals, it is two, and in 320 individuals, it is one. 

The frequency of allele a is

$$\begin{gathered} q=\frac{0\times 85+1\times 320+2\times 295}{1400} \\ q=\frac{320+590}{1400} \\ q=\frac{910}{1400} \\ q=0.65 \end{gathered}$$

Hence, the frequency of allele a is 0.65 because ‘q’ stands for the frequency of ‘a’ allele.