Question

1. Suppose you start graduate school to be a plant physiologist and your first lab rotation is in a lab that studies gibberellic acid (GA) in peas. Unfortunately one of the graduate students in the lab labeled the packets of seeds for two mutants with dry-erase marker instead of permanent marker and the labels rubbed off. One mutant had a defective GA biosynthesis gene and the other had a defective GA receptor gene. Your boss suggested isolating DNA and doing PCR to tell them apart, but you said “just gave me some pots, soil, seeds (including the wild type) and some GA, and I will figure it out for a lot less money.” What would you do and how could you identify which mutant was which? Explain your thinking.

Answer 1

In this case you need three groups: one control and two experimental.

The control is the wild type seed while the two experimental groups are the mutated seeds. Remember that GA is a hormone involved in growth and development. Mutants that are not able to produce GA can be restored to the normal phenotype (wild type) by adding exogenous GA. On the other hand, if the seeds lack of the receptor for GA, they wont be restored by the addition of GA.

So, you will sow one seed of each group and add exogenous GA to the two experimental groups. At the end of the experiment, you will observe that one of these two groups will look similar to the wildtype phenotype. The group that was able to grow by the addition of GA is the mutant that had a defective GA biosynthesis gene while the group that did not grow properly was the mutant that had a defective GA receptor gene.