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.

Key Concepts

Transgenic Plants

Transgenic plants are genetically modified organisms that have had foreign genes inserted into their genome using techniques such as Agrobacterium-mediated transformation. This process allows for the introduction of specific traits, such as pest resistance or herbicide tolerance, which can enhance agricultural productivity and sustainability.

Segregation Ratios

Segregation ratios refer to the expected proportions of different phenotypes or genotypes in the offspring resulting from a genetic cross. These ratios are based on Mendelian inheritance principles, where traits are inherited independently, leading to predictable patterns such as 1:1, 3:1, or other ratios depending on the dominance of alleles and the number of genes involved.

Selectable Markers

Selectable markers are genes introduced into transgenic organisms that confer a trait allowing for the identification of successfully transformed cells. In this case, the herbicide resistance gene serves as a selectable marker, enabling researchers to distinguish between transgenic plants and non-transgenic ones by applying herbicide and observing which plants survive.