
Concept explainers
To explain: The cause of evolution from radial to bilateral symmetry in snapdragon flowers.
Introduction: Snapdragon plant is also known as dragon flower. Antirrhinum is the name of the genus of this plant. It belongs to the family Scrophulariaceae. Snapdragon and its relative species have bilaterally symmetrical flowers. However, the ancestors of snapdragon had radially symmetrical flowers.

Explanation of Solution
Mutation in the cycloidea gene causes radial symmetry in the snapdragon flowers. It indicates that mutation in this gene was present in the ancestors of snapdragons, and because of it, they had flowers with radial symmetry.
However, it cannot be concluded that a mutation in this gene is the only reason which resulted in bilaterally symmetrical flowers. There might be another factor such as adaption. There is also a probability that snapdragon plants lost cycloidea gene during evolution and hence, was not able to produce flowers with radial symmetry.
To explain: Whether the evolution from radial to bilateral symmetry in snapdragon flowers is saltation or not.
Introduction: Snapdragon plant is also known as the dragon flower. Antirrhinum is the name of the genus of this plant. It belongs to the family, Scrophulariaceae. Snapdragon and its relative species have bilaterally symmetrical flowers. However, the ancestors of snapdragon had radially symmetrical flowers.

Explanation of Solution
Saltation in biology stands for any abrupt and immediate evolutionary changes. The evolution of bilateral flowers in snapdragons can be considered as saltation. This is because the deletion of radial symmetry in snapdragon flowers was very rapid. The loss of a single gene resulted in a completely opposite symmetry, which is abrupt. Hence, it is a type of saltation.
To explain: The other possible histories of the evolution of bilaterally symmetrical flowers that are not saltational, but are compatible.
Introduction: Snapdragon plant is also known as dragon flower. Antirrhinum is the name of the genus of this plant. It belongs to the family, Scrophulariaceae. Snapdragon and its relative species have bilaterally symmetrical flowers. However, the ancestors of snapdragon had radially symmetrical flowers.

Explanation of Solution
There are many possible histories related to the evolution of bilaterally symmetrical flowers such as adaptation. It might be a possible reason that flowers of snapdragon plant faced an extreme environment and due to this, they adapted themselves to bilateral symmetry. This is not saltation as there is no abrupt change. Adaptation occurs over a long period of time. It is a compatible evolution that occurred in correspondence to a changed environment.
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Chapter 20 Solutions
Evolution
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