Imagine you do a test cross between a purple- flowered pea plant having serrated leaves (both dominant traits) and a white- flowered pea plant having smooth edges. If the purple- flowered plant is heterozygous for both traits, the expected ratio in the offspring is 1 purple- serrated:1 purple- smooth:1 white- serrated:1 white- smooth. Instead, you see 7 purple- serrated:1 purple- smooth:1 white- serrated:7 white- smooth. What is the explanation of this ratio?
A) There has been a mutation during the cross. B) There is incomplete dominance. C) The genes are sex- linked and inherited by incomplete dominance. D) The genes are linked.