In Arabidopsis, flower development is controlled by sets of homeotic genes. How many classes of these genes are there, and what structures are formed by their individual and combined expression?

Homeotic genes are a group of genes responsible for the regulation of development in organisms. They play a significant role in determining the identity of various structures during development. In the context of this exercise, we are focusing on the homeotic genes that control flower development in Arabidopsis, a plant model organism.

There are three classes of homeotic genes that control flower development in Arabidopsis. These classes are classified based on their specific function and the structures they determine during flower development. They are A-class, B-class, and C-class homeotic genes.

A-class genes are responsible for the development of sepals, the outermost whorl of the flower, and petals, which are the next whorl inward. When A and B-class genes are expressed together, they lead to the formation of petals. B-class genes have a role in the development of petals and stamens, the male reproductive structures of the flower. When expressed with C-class genes, B-class genes contribute to the formation of stamens. C-class genes play a part in forming the carpel, the female reproductive structure, as well as the floral meristem located at the tip of a developing flower. When there is a lack of A-class gene expression, C-class genes direct the formation of the carpel.

1. A-class gene expression alone is responsible for the development of sepals. 2. A-class and B-class gene expression together lead to the formation of petals. 3. B-class gene expression alone contributes to the formation of stamens. 4. B-class and C-class gene expression together also contribute to the formation of stamens. 5. C-class gene expression directs carpel and floral meristem development, especially in the absence of A-class gene expression. In summary, there are three classes of homeotic genes (A-class, B-class, and C-class) that control flower development in Arabidopsis, and their individual and combined expression determine the development of sepals, petals, stamens, carpels, and floral meristem.