Question

Predict the flower phenotypes of the mutant plants listed below. Briefly explain your answers. If it is easier, you may upload a drawing of a "box diagram" to represent A, B, & C fields to show which functions act in the different whorls.

A) ag mutant

B) ap2 pi double mutant

C) ap3 ag double mutant

Answer 1

A diagram of the ABC model, consisting of different class of genes and the structure they form has been given below-

(Se- sepal, pe- petal, st- stamen, ca- carpel).

The A class genes consists of Apetala1 (AP1) and Apetala2 (AP2), B class genes include Apetala3 (AP3) and Pistillata (PI) and the C class genes include Agamous (AG). Class A genes when present, inhibits the function of class C gene and vice versa. Class B gene functions together with either class A or class C gene Taking these into account, we can determine the phenotypes of the given mutants.

A. ag is a C class gene. When class C gene is mutated, class A gene will become functional. So, the genotype will be- A AB AB B. Accordingly, the phenotype becomes- Sepal Petal Petal Sepal.

B. In case of ap2 pi double mutant, both class A and class B are non functional. Therefore, only class C will be expressed. Consequently, the phenotype of the mutant will be- Carpel Carpel Carpel Carpel.

C. ap3 ag double mutant means class B and Class C genes are mutated. Thus, only class A gene will be expressed, and therefore, the phenotype of the mutant will be- Sepal Sepal Sepal Sepal.