How Is Large Scale Morphology Determined By Dna

[jake-the-peg]

OK so I know that DNA codes proteins and messenger RNA gets this to Ribosomes use this to create chains of amino acids and proteins

And I know that foetal cells are stem cells and able to become any tissue type.

But how is the large scale shape of something like a hand coded in DNA and translated into a structure during an embryos development.

How does one cell know to become bone when the next one is a blood vessel wall and another neighbour is muscle?

[LazyGun]

Its complicated :)

In short - Hox genes, a whole bunch of related genes which govern the general layout of the body of the animal/human.

http://en.wikipedia.org/wiki/Hox_gene

After that, it comes down to a whole load of inter-related regulatory networks, most of which are still poorly understood. Mitochondrial regulation, for instance. Epigenetics. And then you have relational control; Cells are instructed to stop growing when they meet cells of a different type, signalled by chemical messages. And finally, there is a growth limiter built in, again through genetics, and once a cell has achieved its growth target - it stops.

So how organs are formed and created, how they know when to stop growing, how these organs are laid out within the body are all governed by a complex inter-relationship between all of the above systems, and some I have not mentioned for simplicity.

You might also be interested in this discussion, taken from "The Naked Scientist" forums, on exactly your issue.

Scan down until you see the contribution from "Nizzle" (14/09/2009 05:25 ish) who offers a more detailed overview of this process.
http://www.thenakedscientists.com/forum/index.php?topic=25283.0

[beso]

Natural selection operates at every scale and time in the development of an organism.

A fully formed organism can only reach reproductive maturity if every step on the way is an adequately functional organism in the environment in which it finds itself. Any that do not succeed in this phase obviously die out long before an adult can be produced.

Consequently the early phases of morphology need have no idea of the grand plan. Hence mammals have pharyngeal slits at the embryonic stage. They just happened to be there in an embryonic plan that was adapted through natural selection.

In practice it helps a lot for everywhere to know which end of the organism is going to be the front and which is the back. That is the first task of the Hox genes.

BTW. One of the fundamental divisions among the bilaterian phyla (protostomes vs deuterostomes) is the difference between those whose first pore in the earliest phases of the embryo go on to form the mouth and those which form the anus first

It is more complex than I have said here and by no means fully understood but it is insightful when considering what goes on in the early phases of embryonic development.

http://en.wikipedia.org/wiki/Embryological_origins_of_the_mouth_and_anus

[jake-the-peg]

Thanks - this was something I'd wondered about but hadn't a toehold as to where to start.

This certainly gives me somewhere to start

The explanation of mRNA gradients makes it hard to explain the lack of symetry.

I suppose there are numerous points of differentiation and it is these that are the really interesting effects

Thanks

[Peter Pedant]

Some interesting questions there j t p

Some fetal cells are stem - but how do they know they are and what are the signals that cause differentiation ? Good question.
Why dont liver cells grow in your eyelid ? In the seventies, they blood filtered and found all sort of cells floating the in the blood. Great Idea - metastasis in cancer is caused by all this. The big difficulty is that the cell rate in blood in those with metastasis is no different to those without.

More luck with the 'plan' and homeobox genes. Basically they found head-neck-thorax-abdo genes arranged in a linear fashion along a strip of DNA.
These genes dont code for a hand, but where the hand is. Disruption in the er seventies (again) caused a fly leg to grow out of its head....

The last question was much easier to answer er in the seventies - all the other genes except bone had been turned off probably by hypermethylation. Now with de-differentiation, the amswer is much more difficult.

Do a course in evo-devo (much loathed by students as there is so much to learn sudduv without end )
and read Nature

Oddly enough - I discussed this in public at the vets - a lady had said the vet has told me my cat doesnt have five pads but eight.

Oh there is a counter that says make a pad, and then stop after five uses. And yours has been stuck onto eight. Since you have five digits on hand and foot, clearly FIVE was decided as a good number before the hand/leg thingey evolved

and one other said : I am a creationist.....

and I said - that doesnt matter....you can see evolution under the microscope in bacteria - so the question now changes from: 'does evolution exist?' to 'how important is it in explaining things ? '

[beso]

Just reading the link I posted. It suggests that the arsh0le has evolved independently on multiple occasions. This would surely be consistent with what we know today. ;-)

[beso]

Cells "know" what they are supposed to be by experiencing their surroundings. The stem cells involved in the construction of blood vessels will become lining cells if they have blood flowing past them and outer layers if they don't.

[beso]

PP //Oh there is a counter that says make a pad, and then stop after five uses. And yours has been stuck onto eight. //

If you look closely at a range of human feet you will see that the structure is more one of big toe, two toes, another two toes. Indeed it is quite common for the two largest toes to be joined for a considerable distance.

I put this down to an earlier structure of three toes of which two subsequently divided.

In the end it all goes back to fish fins which is why the human knee is such a ridiculous design. If God designed it then He was an amateur because He certainly wouldn't have passed engineering.

[Peter Pedant]

beso - the functional unit for the hand is
thumb, index, and three-four-five so according to your plan, function doesnt follow form.

[ I am stuck in the ontogeny recapitulates phylogeny phase, bad, I know, very bad ]

if lobster claw deformity (good images on image-google) is anything to go by, your theory doesnt work (looks like three fingers)
the X rays for the foot form look like three toes (and no hallux)