Question

how does the Hox genes know where to arrange the body parts?

Answer 1

well since no one else has taken a stab at this i guess i will...

its a really tough question, but basically the body uses chemical gradients (mostly in the form of growth factors) that allows cells to recognize roughly where they are in your body. Think about it this way, if substance x is produced in the top of the body, say in the developing brain of an animal, it will be most concentrated near the top of the animal's body near where it is being secreted. Now suppose substance y is being produced by the developing spinal column on the dorsal side of the animal. Now the body has an effective xy grid that allows the cells to specialize in the right areas. Add one more substance (substance z lets say) and you now have an xyz grid in 3 dimensions that allow cells to develop into organs in the correct areas.

Hox genes respond to these concentration gradients and act as master switches to express different genes, causing cells to specialize in the right spot.

Of course, its more complex than this, but i hope this helps... maybe there is a developmental biologist who wants to give this question a shot?

Answer 2

Yes thank you. But I am more concerned as to how does the growth factors x know that they have to be in the top of the body plan?

Answer 3

This arises from the germ layers that develop during the embryonic stage. Im getting a bit out of my league here, but lets see what i remember...

So when an animal is conceived, it quickly divides and produces the zygote and so on. At some point (not sure on the time frame, but probably only a week or so) some of the cells begin to differentiate. Now it could be any cell, but the first one to begin this process starts to inhibit others so that they cannot become what it is. This is the process that leads to the development of the 3 germ layers: endoderm, mesoderm, and ectoderm.

Once the 3 germ layers form, the body has 3 tissues that can set up 3 axis of a chemical gradient. The neural crest will soon from from the ectoderm (some consider this a fourth germ layer, but in truth it arises from the ectoderm). The neural crest is very important to development as it quickly begins produces hormones and other substances that directs much of the development of the fetus.

Im going to stop here because im shaky on all this as it is, but this is my understanding of what happens. Anyone who knows more, its a fascinating and complex subject and i welcome input/criticism.

Answer 4

Well to start off. Not all living organisms have 3 germ layers. Im going to look up whether this is true:

At some point (not sure on the time frame, but probably only a week or so) some of the cells begin to differentiate. Now it could be any cell, but the first one to begin this process starts to inhibit others so that they cannot become what it is

if it is, than virtually my question would be answered