At the supermarket you typically find three types of onions: red, yellow, and white. when true breeding plants with red onions were crossed to true breeding plants with white onions, all the f1 plants had white onions. in the f2 progeny there were 980 plants with white onions, 250 plants with red onions and 80 plants with yellow onions. how many genes are involved in determination of color in onions?