Posts Tagged ‘chromosome’

Platypus. Poisonous, egg laying mammal with ten sex chromosomes

// October 13th, 2010 // 7 Comments » // Recent Research, Science Communication, Sex and Reproduction, The Realm of Bizzare

Platypus

Image by Urville Djasim

Ah, the elusive platypus. The water dwelling animal with fur, webbed feet and a beak. It may just be the strangest animal on the planet. Not only does it look weird, it’s poisonous, can sense electricity, lays eggs and secrete milk through their skin, and have an excessive number of sex chromosomes.

It’s poisonous.
It is SERIOUSLY poisonous. The males have poison barbs under their front feet which they mainly use during the spring breeding season. One scratch from these babies and you will be in terrible agony.

My friend studied platypuses (yes, that’s the plural I checked) in honours and her colleague injected himself with platypus venom in the name of science. For months he had excruciating pain for months which did not respond to any painkillers, including morphine. Because of this quality, platypus venom could help scientists develop drugs which work differently to our current repertoire.

Research into platypus venom is lacking because it is hard to come across samples. But just last month researchers identified 83 possible venom genes using DNA extracted from an active venom gland. Some of the genes are similar to those in snakes, pufferfish and starfish. Now the platypus hardly evolved from a starfish. Instead, it’s an example of convergent evolution, traits that arise separately in different species and give a selective advantage. Illustrious journal Nature says platypus venom confirms the convergent evolution theory for venom. (Research paper Whittington CM, & et al (2010). Novel venom gene discovery in the platypus. Genome biology, 11 (9) PMID: 20920228)

Electroreceptor bill
Sharks use electroreception to find prey by sensing the electricity animals have in their body. Monotromes (mammals that lay eggs) including platypuses and echidnas, are the only mammals with the same ability, and the platypus is the strongest. Closing its eyes and nose when it dives, the platypus relies almost entirely on electrolocation and touch to find the tasty crustaceans it snacks on. Sharks and platypuses are hardly related, making this another yet another example of convergent evolution.

Electroreceptors are located in rows on the bill, which might help it find prey by noticing which receptors pick up the electricity first. We do the same thing with our ears, hearing noises at slightly different times tells us which direction the sound is coming from. When the platypus hunts, it moves its bill side to side, which might reveal how far away the prey is. It’s similar to how pigeons bob their head for depth perception.

Image by TwoWings

Laying eggs
A female platypus has two ovaries, but only the left one is functional. Why? We don’t know.

Eggs spend 28 days developing inside their mother’s body and 10 days outside. The babies (often called puggles) are born with teeth, which drop out as they mature.

The mother produces milk, but she doesn’t have teats or nipples. Instead puggles lick or nibble on her skin to drink, gaining nutrients and probably an immune system. Living in mud, platypuses are born with no immune system, making them worse off than human babies which have immature immune systems at birth and rely on colostrum to boost their protection.

Sex chromosomes
Since the platypus genome was sequenced in 2008, we know a bit about these strange sex chromosomes. We know that they are more similar to birds than mammals, suggesting that our own mammal-like reptile ancestors might have had sex chromosomes like the birds of today. But there’s one big difference that makes the platypus unique.

They have ten sex chromosomes. Males have five X and five Y. Females have ten X. Humans, in fact, almost all mammals have only two. During platypus sperm production, the sex chromosomes pair up as X1Y1, X2Y2, X3Y3, X4,Y4, X5,Y5, so they can split evenly to make sperm that have 5X or 5Y. Phew. After all that, I’m surprised the males have any energy left for mating.

What is the synthetic cell?

// May 22nd, 2010 // 1 Comment » // How Things Work, Recent Research

Two days ago scientists at J. Craig Venter announced the creation of the first self-replicating synthetic cell, a bacteria with DNA made in a lab. How did they do it, and what does it mean for us in the future?

First up, the scientists didn’t make life out of nothing, and they didn’t make a new species. They recreated a bacteria that already existed, and developed the techniques to do it.

The bacteria is Mycoplasma mycoides. It’s a parasite which lives in cows, and some subspecies cause cow lung disease. It has a circular chromosome made of just under 600,000 base pairs, making it a small genome.

The scientists had the genome sequence of M. mycoides and split it into bite-size portions and then synthesised. Synthesising DNA is nothing new, scientists have been able to write DNA code for quite a while, and can write whatever code they want to.

These little chunks were put into yeast, which can be forced to absorb little bits of DNA. Inside the yeast, the chunks can be sewn together. It’s called recombination. The resulting medium chunks were taken out and put into more yeast to be sewn together making large chunks. There were 11 large chunks were put into more yeast, and sewn together into one complete genome.

Along the way and at the end they checked the code was right by doing PCR tests, genetic fingerprinting made famous by CSI.

Result: A synthetic genome, written by a computer and put together in yeast sweatshops.

Now they had to get it into a bacterial cell. At first they tried to put the DNA into bacterial cells of a similar species, M. capricolum. They ran into trouble at first, because the DNA they had was unmethylated (lacking methyl groups) and the bacteria destroys DNA which is unmethylated. It’s a clever defense mechanism, and they got around it by methylating the DNA before putting it in.

Finally success. The synthetic genome was put into an M. capricolum bacteria where it replaced the normal genome. The bacteria were controlled by the new, synthetic chromosome and were able to replicate billions of times.

What does it mean for us in the future? The technology these guys have developed could be used to alter the DNA of bacteria and make them do new things. From medicine to clean water, the benefits could be huge. We already have this ability to some extent, but it opens up some new doors.

Some organisations have raised concerns about the work. Could a new bacteria be unleashed and take over the world? Probably not. It’s hard to predict how new genes will work in cells, and everything is linked together in a way we don’t understand now. Too much tinkering to the genome will probably not be tolerated by the cell. And if it did get outside, it would probably be extinct pretty quickly because it doesn’t have thousands of years of evolution to prepare it for the world.

If it did get out, we could track it back to the company in charge. These guys watermarked their genome by adding some quotes into the DNA/protein code. Now that’s just epically geeky!

ResearchBlogging.orgGibson, D., & et al (2010). Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome Science DOI: 10.1126/science.1190719






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