Ten Sex Chromosomes
While humans have 2 sex chromosomes (XX or XY), platypuses have 10 â the most complex sex determination system known in mammals.
The platypus is famously weird: a venomous, egg-laying mammal with a duck bill and beaver tail. Its reproductive biology is equally strange.
While humans have a simple XX (female) or XY (male) system, platypuses have 10 sex chromosomes â five X chromosomes and five Y chromosomes. Females are XXXXXXXXXX, males are XYXYXYXYXY. This is the most complex sex determination system known in any mammal.
The platypus system shares features with both birds and reptiles, hinting at the ancient evolutionary history of mammals. Some of their sex chromosomes are similar to bird sex chromosomes rather than typical mammal ones.
As one of only five surviving monotremes (egg-laying mammals), platypuses bridge the gap between reptiles and mammals: - They lay leathery eggs like reptiles - They produce milk like mammals (but through skin patches, not nipples) - They have venomous spurs like some reptiles - They nurse their young like mammals
The eggs are incubated for about 10 days, then hatch into tiny, helpless babies that continue developing while nursing for 3-4 months.