In a population of 1000 flowering plants there are two possible alleles for flower color, one dominant and one recessive. 400 plants are homozygous dominant, 200 plants are heterozygous, and 400 plants are homozygous recessive.

What is p in this population, if p represents the frequency of the dominant allele?

Question

In a population of 1000 flowering plants there are two possible alleles for flower color, one dominant and one recessive. 400 plants are homozygous dominant, 200 plants are heterozygous, and 400 plants are homozygous recessive.

What is p in this population, if p represents the frequency of the dominant allele?

BlackTom AI · Accepted Answer

We start by restating the problem to ensure clarity: In a population of 1000 flowering plants with two alleles for flower color (one dominant, one recessive), the genotype counts are 400 homozygous dominant (AA), 200 heterozygous (Aa), and 400 homozygous recessive (aa). We are asked to determine p, the frequency of the dominant allele A, in this population. The answer options given are: 0.6, 1.0, 0.4, 0.5.

First, compute the total number of alleles present in the population. Each plant has 2 alleles, so with 1000 plants, there are 2,000 alleles in total.

Next, count how many of these alleles are the dominant A allele. From the genotype counts:
- AA (homozygous dominant) individuals contribute 2 A alleles each: 2 × 400 = 800 A alleles.
- Aa (heterozygous) individuals contribute 1 A allele each: 1 × 200 = 200 A alleles.
- aa (homozygous recessive) individuals contribute 0 A alleles.
Total A alleles = 800 + 200 + 0 = 1,000.

Now, p, the frequency of the dominant allele A, is the number of A alleles divided by the total number of alleles:
p = 1,000 / 2,000 = 0.5.

Option-by-option analysis:

- 0.6: If p were 0.6, then the number of A alleles in 2,000 total alleles would be 0.6 × 2,000 = 1,200 A alleles. The observed counts give only 1,000 A alleles, so this value would not match the given genotype distribution. This option is inconsistent with the data and thus incorrect.

- 1.0: A frequency of 1.0 would imply that every allele in the population is the dominant A allele (2,000 A alleles in total). The observed data include 400 aa individuals with zero A alleles, so this cannot be correct. This option is clearly incorrect given the presence of recessive phenotypes/genotypes.

- 0.4: A frequency of 0.4 would correspond to 0.4 × 2,000 = 800 A alleles present in the population. The actual count from genotype data is 1,000 A alleles, not 800, so this option does not fit the data. This option is inaccurate.

- 0.5: A frequency of 0.5 yields 0.5 × 2,000 = 1,000 A alleles, which matches the tally obtained from the genotype counts (800 from AA and 200 from Aa, totaling 1,000). This option aligns with the observed data.

In summary, you evaluate each option against the allele counts derived directly from the given genotype frequencies. The only value that coherently accounts for 1,000 dominant alleles out of 2,000 total alleles is 0.5, while the other options fail to reproduce the observed genotype-based allele tally.

APBIO142-030 with labs 23.01 to 23.02 - Video Quiz

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