Mixed marigold flowers on one plant?
 

I never was especially good in biology, but I am really curious about this.

This summer I have a number of marigold plants that came up via self-seeding from last year. The original plants last summer were small 1' tall plants with reddish-orange flowers and 2.5' tall plants with yellow flowers. I assume there was some cross-pollination to develope the seeds for this year's plants. This year's plants are mostly 2.5' tall, and have flowers ranging from yellow to orange, some flowers are full of petals and others have only a scraggly row or two of petals.

The thing that confuses me is that this range of flowers appears on some individual plants while other individual plants have many flowers all similar in appearance. I would expect variations from plant to plant, but the range of flower colors and petals on some of the individual plants really confuses me.

Where is my education lacking???