At roughly 2.2 billion base pairs, the platypus genome is about two-thirds the size of the human genome, the researchers found. It shares more than 80 percent of its genes with other mammals.
Like humans, platypuses carry an X and a Y chromosome. But unlike humans, the X and Y are not sex chromosomes. "That means we can go right back to the time when our sex chromosomes were just ordinary chromosomes minding their own business and ask well what happened, what made them into sex chromosomes," Graves said.
The researchers revealed the animal has 52 chromosomes, including 10 sex chromosomes.
The genome also included sections of DNA linked to egg-laying and others for lactation. Since the platypus lacks nipples, the pups suckle milk from the mother's abdominal skin.
Another oddity: When paddling through the water, a platypus keeps its eyes, ears and nostrils closed, and its duck-bill serves as an antenna, sensing the faint electric fields surrounding prey. Even so, the platypus genome reveals the animal held onto genes for odor-detection.
The study, which included more than 100 scientists from across the globe, was funded by the National Human Genome Research Institute (NHGRI).