Recently, scientists from the University of East Anglia have discovered exactly which part of the genetic code was responsible for this, though an event that occurred over 51 million years ago. The genes from the Primula genome were mapped and sequenced to find the specific gene cluster responsible for creating the different flower morphs. They discovered that the supergene directly responsible for this is the S locus.
The S locus supergene is a tightly linked cluster of thrum-specific genes that are not in pins. The thrums were shown to be hemizygous, not heterozygous for the S locus. Therefore, the assumption that the homostyles arise by recombination between S locus haplotypes is false.The researchers were also able to determine that the original mutation occurred 51.7 million years ago. A floral homeotic gene was duplicated, then inserted itself in the S locus gene, and then mutated to control the anther position in the flower.
This discovery is of major importance because it gives a better understanding of the pollination mechanism. Even though I was never very interested in plant biology, I found this discovery very eye-opening, especially since it unlocks the secret behind Darwin's observations and studies. I'm looking forward to reading more about this research and plant biology overall.