Slashdot Mirror
Single-Celled Species' Genome As Complex As Ours?
An anonymous reader writes: "A new paper reports on the sequencing and analysis of the genome of a single-celled species known as Tetrahymena thermophila. This ciliate (like the Paramecium people look at in school) has some 27,000 genes, or nearly as many as humans. And despite existing as a single cell, this spcies encodes fantastic complexity and unusual features. For example, it has a primitive immune system that prevents the invasion of foreign DNA. Also, it is able to cordon off its germ cell lineage much as humans do with sperm and eggs. But Tetrahymena does this by having two nuclei within each cell, with one of the nuclei being held in reserve for sex. Basically, this species uses its genome complexity to function like a single celled chameleon, changing its shape and its properties in response to the changing environment. For example, when a new nutrient shows up in its neighborhood this species can build a kit to suck the nutrient in, degrade it, and turn it into cellular biomass quickly. Thus whereas humans use their genomic complexity in part to create a stable environment for the body, this species simply uses a genomic swiss army kit to make do with whatever environment it encounters."
Tetrahymena are non-pathogenic free-living ciliate protozoa. They are common in fresh-water. Tetrahymena species used as model organisms in biomedical researches are T. thermophila and T. pyriformis.
http://en.wikipedia.org/wiki/Tetrahymena
Wincopy
I feel it's worth pointing out that no where in the Origin of Species does Darwin discuss human/great ape/primate evolution. I'm not even certain he used the word "evolution", but don't quote me on that. Also, no true evolutionary biologist has ever said that humans descended from monkeys. It's that whole common ancestor thing. Lot's of branches, not straight line.
Darwin himself had never heard of Mendel's theory of genetics. He proposed that offspring are a "mixture of fluids" from the mother and father.
Not everything in in the genetic code. Those interested can consult the Wikipedia articles about epigenetics and Lewontin's fallacy. They may also read the original article by Edwards. Edwards is a bigger scientist than Lewontin (although less popular). Edwards is a typical British population geneticist with a solid mathematical background. Lewontin is an American Geneticist, well known because he writes popular science,deals with vague issues which are of interest for the general population, etc; his mathematics is not that good.
That's a horrible misunderstanding. The number of genes has nothing to do with complexity of adaptation. Their REGULATION does. That's why ~90% of the human genome is non-coding. Much of the intragenic space is packed with chromatin and transcription regulatory sequences, control sites, etc... etc... etc...
Here's an analogy:
It's similar to saying that sophistication of manipulation is a function of how many fingers one has. That's not correct - you need specific muscle placement, fine motor and sensory function, and huge regions of the brain dedicated to actually using those fingers in order to achieve the mastery of manual manipulation that humans have. Just because an animal has 5 fingers, it doesn't mean it can manipulate objects as well as we do.
No, we can't survive those conditions. However, we use our intelligence to MAKE those places have OUR environment. We build our space suits and our space stations, we build our deep submersibles, etc. We have yet to make it so that a human being can be exposed to those conditions and still function. That's an entirely different level of interaction, and please keep it distinguished. We cannot survive in space exposed, however, we can bring our environment to it.
Long version:
http://en.wikipedia.org/wiki/Evolution_of_the_eye
Short version: We now know that patches of photoreceptive cells can develop without the surrounding structure of the eye. Furthermore, having minimal sight is substantially better than no sight whatsoever, so even "half an eye" is workable from an evolutionary perspective.
So incremental development is possible, beginning with a retinal precursor, and slowly developing layers of complexity that give rise to the various types of eye (for example, human eyes and compound eyes, which are dissimilar in configuration, but serve the same function).
Erotic is when you use a feather. Exotic is when you use the whole chicken.
Why the hell is this in the IT section?
The human eye has a "design" error, in that the photosensitive layer is not in front, there are other cells above them.......
Actually, the mammalian (human) eye is optimized for the metabolic loads it requires. It turns out that there is no higher area of metabolism in your body than there is at the photoreceptor/retinal pigment epithelium interface. It is a highly oxidative environment and evolutionarily, you need the apposition of the photoreceptors up against a layer of cells that can deal with the shed outer segments and the metabolic loads induced by rod photoreceptors. The other advantage is that you can snuggle the photoreceptors up to these cells that have a direct connection (diffusion) to a vascular layer. If it were backwards, the blood vessels would get in the way of the image formation and cast shadows.
In mollusks, OTOH, the outer layer of cells is the photosensitive one. The eye is more sensitive to light, has no blind spot, and allows for more data processing in the retina itself. That may be one of the reasons why octopuses are so good at camouflage, their eyes are very sensitive.
Octopuses, squid, and cuttlefish have fairly sophisticated retinas that is true and you are correct about their anatomy. However, they do not process the same metabolic loads that the mammalian retina does and thus do not require the same degree of buffering, care and feeding that mammalian photoreceptors do. You have to be careful about using "sensitive" to describe eyes as that descriptive is dependent upon lots of things. Typically in most retinas it has to do with the ability of the opsin to capture a photon and the cell the opsin is in to transduce that signal.
All this is one more argument for evolution and against the "intelligent design" theory.
Intelligent design (ID) really does not even factor into either argument. ID is a religiously/politically motivated belief, not a theory that can be tested.
Visit Jonesblog and say hello.
Funny, I'm listening to Dr. Waston's 50th anniversary book of the double helix (2003) CDBook this month.
The human genome betting pool paid off at 23,299 genes in 2004, though some people suspect a few more. Most sequenced mammals appear to have about 3 billion base pairs and 25K genes. The highest animal number I heard was the puffer fish at 39K genes. The record appears the amoeba dubia at 670 billion base pairs.
Mammalian gene storage and expression is more complicated than bacteria. Dr. Watson said the typical gene is divided into eight segments (exons) with some approaching 30. Plus these may code for multiple proteins. Some biochemical stores sell DNA genes with the introns removed (cDNA). These are made from RNA templates found cells and turned back into continginuous DNA. There are about twice as many cDNAs for a mouse than there are genomes.
> The resolution is very poor in the receptors that work in colour, and the high-resolution ones don't work at high light levels.
/only/ work at high light levels.
I don't know where you have got this information from, but it is absolutely not true. The fovea is the high resolution region of the retina and contains only "red" and "green" cones. The peri-foveal region contains a smattering of blue cones too. These are the receptors responsible for high-acuity color vision and they
> The connection to the is seriously underspec'd (by a couple of orders of magnitude.
The connection is fine because it effectively transmits the log of intensity not intensity. In fact, with light-adaptation at different conditions (something done by the retina not pupil diameter as everyone seems to think) your eye can handle light intensity conditions over a a staggering 11 orders of magnitue (startlight to a bright noon sun).
Many people may not know this but the number of genes and amount of DNA that a particular species has does not necessarily correlate to genome complexity. Salamanders have almost 10x the amount of DNA as humans, but the amount of coding DNA is not even close to the amount of coding DNA for humans. Genetics is not that simple. It is interesting though that this organism can pick and choose which genes to express at certain times.
Absolute power corrupts absolutely. indymedia
It basically comes down to a cost/benefit analysis. If a cell/organism can benefit from a fat genome, it will. New research about "junk DNA" finds that it is not really junk, but a stored-up mass of potentially usable DNA to turn on and off as needed by essentially modifying a Goto statement(s) to skip or use them over generations. Mutations may affect where the Goto jumps to, but by packratting old genes it does not have to evolve old lessons from scratch again..
If our ancestors did not have to run from or hunt fast mean animals, then perhaps our genome would pile up with "in-case" genes also. Appearently this organism uses flexibility instead of being the leanest to survive. Humans more or less also use this strategy, but by learning with brains, not via DNA. DNA is essentially a kind of long-term brain.
Table-ized A.I.
What if on some level, our cells construct egg/sperm cells based on macroscopic-level environmental conditions?
Don't give up the day job.