Why would you end up with a double bar graph if you would plot the frequencies of two phenotypes of a single-gene trait?

A double bar graph is used to compare the frequencies of two phenotypes of a single-gene trait because it allows for a clear visual representation of the differences between the two groups. Each phenotype can be represented by a separate bar, facilitating a direct comparison of their respective frequencies. This format helps to easily identify trends, patterns, or discrepancies in the distribution of the traits within a population or sample. Additionally, it makes it easier to analyze the relationship between the two phenotypes, especially in studies related to inheritance and genetics.