Chapter 15, Problem 23P

You have generated three transgenic lines of maize that are resistant to the European corn borer, a significant pest in many regions of the world. The transgenic lines (T $1$ in the accompanying table) were created using Agrobacteriummediated transformation with a T $\text{-}$ DNA having two genes, the first being a gene conferring resistance to the corn borer and the second being a gene conferring resistance to a herbicide that you used as a selectable marker to obtain your transgenic plants. You crossed each of the lines to a wild $\text{-}$ type maize plant and also generated a T $\text{2}$ population by self $\text{-}$ fertilization of the T $1$ plant. The following segregation results were observed (herbicide resistant: herbicide sensitive):

Explain these segregation ratios.