Some plants divide the stamens and pistils into separate strains and have X and Y sex chromosomes, similar to humans. If you have XY, you will be male, and if you have XX, you will be female.Such plants are thought to have evolved from plants that attach stamens and pistils to a single strain, and Hirohanomantema of the family Caryophyllaceae is a typical example. The Y chromosome requires a gene that suppresses the development of the pistil as a sex-determining gene and a gene that promotes the development of the pistil.Since the Y chromosome of Hirohanomantema is 10 times larger than the human Y chromosome, it was difficult to examine the gene sequence.

　The collaborative research group irradiates the Y chromosome with a type of radiation called a heavy ion beam to cause abnormalities, creating strains that have both stamens and pistils, and strains that do not have either.We succeeded in creating a genetic map on the Y chromosome by investigating the correspondence between the features that appeared and the site where the chromosomal abnormality occurred.Furthermore, when compared with the gene map of the X chromosome that had already been clarified, it became clear that the corresponding genes were completely reversed.This means that naturally occurring gene recombination is suppressed.This fact is an important discovery when considering the evolution of sex-determining genes.

　It is thought that the suppression of gene recombination may be the cause of having the Y chromosome.In the future, by conducting a more detailed investigation, we will investigate which genes were acquired in what order, and how the strains were divided between males and females accordingly.