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?

After researching Arabidopsis homeotic genes, we find that these genes are responsible for the development of floral organs in plants. There are three classes of homeotic genes namely A, B, and C.

The A class genes, when expressed individually, lead to the development of sepals in the outermost whorl of the flower. B class genes, when expressed individually, are responsible for the formation of petals in the second whorl. Finally, the C class genes, when expressed individually, lead to the development of carpels in the innermost whorl of the flower.

The flower structures are formed based on the combined expression of these classes of homeotic genes. The combinations are as follows: 1. A class + B class genes: They lead to the development of petals in the second whorl of the flower. 2. B class + C class genes: They result in the formation of stamens in the third whorl of the flower. 3. A class + C class genes: They lead to the development of normal flowers with all the different whorls and the organs they contain (sepals, petals, stamens, and carpels). In conclusion, there are three classes of homeotic genes in Arabidopsis, namely A, B, and C. Their individual expression leads to the formation of sepals, petals, and carpels, respectively. The combined expression of these genes results in various flower structures including normal flower development with all whorls and organs.