BioProject

Ornithorhynchus anatinus, or duck-billed platypus, is an important model organism for developmental, evolutionary, and genomic studies. More...

Ornithorhynchus anatinus, or duck-billed platypus, is an important model organism for developmental, evolutionary, and genomic studies. The platypus and two species of echidna comprise the monotremes (prototherian mammals). Monotremes diverged from therian mammals (marsupials and placentals) approximately 210 million years ago and, not surprisingly, retain a mixture of reptilian and mammalian features. Monotremes are best known for their mixture of primitive and derived reproductive traits. For example, monotremes lay eggs but also have mammary glands. In platypus, eggs are nourished in the uterus for approximately 28 days and then externally incubated for 10 days. As in birds and other reptiles, the platypus karyotype consists of a few macrochromosomes and many microchromosomes. Platypus have 52 chromosomes. Males are heterogametic with 21 paired chromosomes and 10 unpaired chromosomes (X1-5 and Y1-5). During meiosis these unpaired chromosomes form a linked chain of elements. Though the sex determination system of monotremes is still incompletely understood it offers tantalizing clues to the ancestral sex determination system of birds and placental mammals.