The papaya plant carries the youngest Y chromosome ever found, reports a research team. That sex chromosome is so new evolutionarily that it doesn't have the stripped-down style of full-fledged Y chromosomes.
The papaya chromosome carrying the gene for maleness doesn't look different from the plant's other chromosomes, explains Ray Ming of the Hawaii Agriculture Research Center in Aiea. Fine-scale genetic mapping indicates two traits characteristic of Y chromosomes, Ming and his colleagues report in the Jan. 22 Nature. The papaya's male-determining region doesn't swap genes with the corresponding region of its partner chromosome, and the Y region shows signs of genetic degeneration.