Question

How does the ABC Model of Plant Development work? What are A genes, B genes and C genes?

Answer 1

The ABC model of plant development is a model developed by scientists in which angiosperms i.e. flowering plants produce a pattern of gene expressions in meristems which would lead to the appearance of a flower. In this model scientists used a series of homeotic mutants, and double and triple mutants, to establish a predictive model of organ specification in development of flowers.

Complete answer:
The ABC model was developed to understand the genetic approach to flower development. It was developed in 1991. The ABC model of flower development in flowering plants describes that the development of sexual organs of plants are regulated by three classes of genes. These classes of genes are Class A , Class B and Class C genes.
While analyzing the homeotic mutation in flowers Coen et al. found that three genes are basically responsible for development of the structure of flowers. They showed that the flowering plants which are very distantly related to each other use the similar mechanism to develop the pattern of formation of flower organs. Those distantly related flowering plants were Arabidopsis thaliana and Antirrhinum majus.
-Class A gene will develop the apical meristem which is the region from where the flower develops into sepals.
-Class B genes are expressed on the cells with the Class A gene will later form petals.
-Class C genes are expressed with Class B genes to develop the formation of stamens which is the male reproductive part of the flower. But if they are expressed alone into the cells they will later form a carpel which is the female reproductive part of the flower.

Note: Homeotic mutation occurs when the petals are replaced by a second whorl of sepal like organs. This mutation is very rare in flowering plants. It is found in a plant named Clarkia which belongs to the Onagraceae family. This mutation is governed by a single recessive gene.