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 (T₁ in the accompanying table) were created using Agrobacterium-mediated transformation with a T-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-type maize plant and also generated a T₂ population by self-fertilization of the T₁ plant. The following segregation results were observed (herbicide resistant : herbicide sensitive):

Cross                                     Line 1    Line 2    Line 3
Transgenic (T₁) × wild type       1:1        3:1         5:1
Self-cross (T₂)                           3:1      15:1       35:1

Explain these segregation ratios.