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In pea plants, purple flower color, $C$, is dominant to white flower color, $c$. The table shows the frequencies of the dominant and recessive alleles in three generations of peas in a garden.



\begin{table}

\captionsetup{labelformat=empty}

\caption{Allele Frequency for Flower Color in Peas}


Generation		$p$$q$

1		0.60.4

2		0.70.3

3		0.80.2




\end{table}



Which statement is a conclusion that may be drawn from the data in the table?


AThe population of pea plants in the garden is in Hardy-Weinberg equilibrium.
BThe population of pea plants in the garden is growing larger in each generation.
CThe decreasing frequency of white-flowered alleles shows that the population is drifting.
DThe increasing frequency of purple-flowered alleles shows that the population is evolving.

Verified Answer :

  • Hardy-Weinberg equilibrium requires allele frequencies to remain constant over time.
  • The provided data shows that allele frequencies change across generations (\(p\) increases, \(q\) decreases).
  • Any change in allele frequencies over time is defined as evolution.
  • Final Answer: The increasing frequency of purple-flowered alleles shows that the population is evolving.

Explanation

  1. Analyze the allele frequencies and Hardy-Weinberg equilibrium

To understand whether the pea plant population is evolving, we must examine the definitions of the terms provided. The Hardy-Weinberg equilibrium is a state where allele frequencies in a population remain constant across generations. If the population were in equilibrium, the values of \(p\) and \(q\) would not change. However, as the table shows, the frequency of the dominant allele \(p\) increases from \(0.6\) to \(0.8\) over three generations, while the frequency of the recessive allele \(q\) decreases from \(0.4\) to \(0.2\). Because the allele frequencies are changing, the population is not in Hardy-Weinberg equilibrium.

  1. Determine if the population is evolving

In biological terms, evolution is defined as a change in the allele frequencies of a population over time. Since our data shows that the allele frequencies for the pea plants change from one generation to the next, we can conclude that the population is undergoing evolution. The data does not provide information about the total size of the plant population, so we cannot conclude whether it is growing larger or smaller. While genetic drift can cause changes in allele frequencies, it is specifically a random process; simply observing a change in frequencies is primarily evidence of evolution, without assuming the specific mechanism (like drift or natural selection).

  1. Select the correct conclusion

By comparing the options provided to our conclusion:

  • The population is not in Hardy-Weinberg equilibrium because allele frequencies change.
  • The table contains no data about the total number of plants, so the growth rate is unknown.
  • The term "evolving" is the most accurate scientific description for a population with changing allele frequencies.

Therefore, the most appropriate conclusion is that the increasing frequency of the purple-flowered alleles indicates that the population is evolving.

Examples

This concept is fundamental in genetics and ecology. For example, if a biologist tracks a specific trait in an endangered species over several years and notices that the frequency of a certain allele is steadily increasing, they can quantify the rate of evolution within that population and determine if conservation efforts are helping to maintain genetic diversity or if the population is adapting to new environmental pressures. Understanding these shifts helps scientists make informed decisions about preserving biodiversity. If the allele frequencies were stable, we could calculate the expected genotype frequencies using \(p^2 + 2pq + q^2 = 1\), allowing us to predict the proportion of different flower colors in the next generation.

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