By Ricki Lewis
Move over Craig Venter and James Watson, the latest celebrity to have her genome sequenced is Glennie, a member of Ornithorhynchus anatinus. She hails from New South Wales, Australia.
When the planners of the human genome project set aside funds for sequencing the genomes of others, I was glad that the enigmatic platypus made the list. Occupying a key branchpoint on the evolutionary tree, the platypus is a hodgepodge of parts borrowed from birds and reptiles, and echoed in the vastly more numerous placental mammals. The curious web-footed and furry, egg-laying and lactating beasts diverged from the most recent shared ancestor of all mammals about 166 million years ago, heading in a different direction from its pouched and placental brethren. The reports on the platypus genome are published in Nature and Genome Research.
Why sequence the platypus genome? Let me count the ways.
1. To all Intelligent Designers bemoaning the lack of so-called transitional forms, take a look at Glennie either her body or her genome.
2. The platypus genome holds clues to our own evolution. What have our genomes and bodies lost that the platypus retains, and what have we gained?
3. The male platypus discharges powerful venom from spurs on his hind legs. He uses the stuff for mating and marking territory, but the venom is a beta-defensin an antimicrobial. Platypus venom and reptilian venom diverged from an ancestral recipe.
4. If the leg venom doesnt yield a drug for us, maybe another antimicrobial represented in the platypus genome will cathelicidin. Researchers suspect it protects the very immature baby platypuses. Use in human preemies?
5. Nearly a third of premature baby boys have undescended testicles. So do platypuses, making them a missing link of sorts in the evolution of this reproductive trait. Other mammals have scrotums, which cool developing sperm.
6. The platypus genome is riddled with mobile genetic elements jumping genes. Such genes lie behind several human disorders.
7. The platypus has a sense or two that we do not. The flat nose can detect electrical fields that prey emit on river bottoms. Surely someone can find a use for this skill.
8. Pheromones not quite hormone, not quite aphrodisiac, animals use these biochemicals in mating, among other activities. A collection of receptors that form a vomeronasal organ sense pheromones, and the systems have been well-studied in rodent urine, elephant trunks, cat grimaces, and flicking serpent tongues. Whether or not humans retain use of this body part after birth is controversial.
9. Smell. The platypus has an impressive number of odorant receptor genes. Why is this so, for an animal that spends much of its time underwater?
10. For those interested in stats, here are the facts: the platypus genome is 2.2 billion base pairs, with 18,500 genes, and 52 chromosomes, 10 of which determine sex. The genome is remarkably similar in sequence to those of mice, dogs, opossums, chickens, and anole lizards.
Go Glennie!
Ricki Lewis is the author of the novel Stem Cell Symphony and the textbook Human Genetics: Concepts and Applications, now in its 8th edition. She is a fellow of the Alden March Bioethics Institute.