Maize Domestication: A Decision to Branch Out

A student observes a corn plant, noticing its impressive structure with very few lateral branches, which allows for high-density planting. This is contrasted with its wild ancestor, teosinte, which has many more branches. During domestication, humans selectively bred plants for less branching.

The gene responsible for branching is identified as Tb1, short for teosinte branched one. A hypothesis is formed that Tb1 causes plants to branch more, and in maize, this gene somehow isn't functioning as expected.

To test the hypothesis, a loss-of-function experiment is proposed using a Tb1 mutant plant, where the gene is not functional. The control group is a normal plant, and the experimental group is the mutant. When observing the mutant, it shows significantly more branches, leading to a revised understanding that Tb1 inhibits branching.

The experiment demonstrates an inhibitory connection: decreasing the independent variable (Tb1 gene) leads to an increase in the dependent variable (branching). This loss-of-function experiment concludes that Tb1 is required, or necessary, to inhibit branching.

A gain-of-function experiment explores what happens if Tb1 expression is increased. The expectation is less branching. This type of experiment concludes that Tb1 is sufficient to inhibit branching. Performing both loss-of-function and gain-of-function experiments provides a stronger case that Tb1 is a major player in this process.

Considering where the Tb1 gene is expressed, it's expected to be found in cells that have the potential to form branches. Where Tb1 is present, those cells will not form branches. This observational evidence is called correlation, as the gene expression level was measured, not manipulated.