May 12 at 6:06pm by Aileen
…after all these years
That great practical joke that life’s designer [be it blind nature or purposeful god] played is still with us to confound orderly notions of biological evolution. The genome of Australia’s duck-billed platypus has been sequenced by an international group of scientists led by researchers at Washington University School of Medicine in St. Louis.
The venomous, egg-laying, duck-billed, web-footed, beaver-tailed mammal is one of the earliest offshoots of the mammalian lineage from when it split off from primitive ancestors some 166 million years ago. The genome confirms the chimeric status of this odd animal which displays traits of reptiles, birds and mammals.
As part of their analysis, researchers compared the platypus genome with human, mouse, dog, opossum and chicken genomes. Chicken genome was chosen because it represents a group of egg-laying animals that includes extinct reptiles that passed on much of their DNA to mammals over the course of evolution. When analyzed, the genetic sequences for venom production in the male platypus was found to have arisen from duplications in a group of genes evolved from ancestral reptilian genomes. They hypothesize that duplications in those very same genes led to the evolution of venom independently in modern reptiles.
The project involved sequencing about 2.2 billion base pairs and 18,500 genes. The Platypus has 52 chromosomes and an unusual 10 sex chromosomes. The platypus X chromosome also bears a striking similarity to the sex chromosome of birds.
Final conclusion? The duck-billed platypus is just as bizarre a mix-and-match critter genetically as it appeared to be when the first specimens were shown to the scientific community some 200 years ago. Skeptics then believed the animal was someone’s idea of a practical joke hoax. Turns out it really is a genetic practical joke, but it comes as-is in nature.