The control of flowering is a complex process involving several key regulatory genes. Some statements on flower development are given below:

P. Two major types of genes regulate floral development: meristem identity genes and floral organ identity genes.

Q. The important genes in Arabidopsis that play key regulatory roles in meristem identity are: APETALA1, LEAFY and SUPPRESSOR OF CONSTANS1.

R. The genes that determine floral organ identity were discovered as floral homeotic mutants.

S. Most plant homeotic genes belong to a class of related sequences known as FAD box genes.

Which one of the following combinations of the above statements is correct?