The Dragonseed is a thing which altered the DNA of the Mandarin that makes him able to wear the rings and that makes him not just human but Part-Makluan. The Dragonseed can only be given if that person is worthy to wear the rings by the Makluan.
When a Makluan retrived the rings from the overlord of the Makluans, he escaped to a mysterious planet called Earth. Once there, he looked for a man who will use the rings for good. The Makluan found a man named Khan, who was kind, generous and worthy enough to wear the rings. The Makluan put the dragonseed in Khan that made Khan known as the first Mandarin. Throughout the family, they had the dragonseed inside them. making them Part-Makluan. The only known Part-Makluan is Gene Khan, who is the last of the family and known as the only Part-Makluan on the Earth.