chromosomes - (Feb/10/2007 )
I copied my friend's notes on biology, here are some places that i don't really understand, hope you can help me, thanks.
1. How do cells become specialized or differentiated? Here specialized cells means the cells which develop so as to become adapted to a specific function or environment? And differentiated cells means the cells which change from relatively generalized to specialized kinds, during development? I am not so sure about their definitions.
2. Some genes on the chromosomes turn on or off to produce specific, specialized tissues. What does it mean by 'turn on or turn off' regard to chromosomes?
3. Only the part of the chromosome that programs to make bone will be turned on. I don't understand, either.
I didn't learn the knowledge of this topic, so hope you can answer my specific questions toward the topic. Thanks for your patience.
hi MIA6,
many of the answers to your questions can be found in a good molecular biology textbook.
I suggest you have a look there first, and maybe get your friend to explain it to you also.
Hi MIA6,
Basically you really need to read a chapter about differentiation in a good textbook.
Nevertheless I will try and give you short answers to help you out:
I think your greatest problem is the definition of "specialized" and "differentiated".
In the question above, both terms (specialized and differentiated) mean the same thing, and you basically got it right:
"differentiated cells" means the cells which change from relatively generalized to specialized kinds during development.
BUT:
The answer should be focussed on HOW the cells specialize/differentiate, or more precise: WHAT triggers the differentiation/specialization?
Now get a textbook and find out what makes cells differentiate (such as nutrients/metabolites in the cell's environment , or signals from surrounding cells)
There are many many maaany more - you may also find info on the internet, but a textbook will be more compact and thus faster... ;-)
"turn on or turn off" in this question does NOT refer to the chromosomes, but to the genes!
The sentence would be less confusing like this : Genes are located on chromosomes. Some genes turn on (or off) to produce specific, specialized tissues.
A gene can be either "on", meaning it is being transcribed into RNA (& translated into protein ),
or "off", meaning there is no RNA and no protein being copied.
For specialization/differentiation into tissues, some genes have to be "on" and some "off".
Which genes have to be "on" and which ones "off" depends on the tissue type the cell is differentiating into.
On a chromosome there is a lot of information. not all information is used at the same time.
Say (for example!!!) the genes for bone and skin were on the same chromosome.
If the cell differentiates into a bone cell, then the bone genes are "on", and the skin genes are "off".
If the cell differentiates into a skin cell, then the skin genes are "on", and the bone genes are "off".
Conclusion: All cells HAVE the same chromosomes and genes, but they USE different parts or regions of them.
Hope I could help.
cheers,
Goofy
@MIA6: It would of course also help if you came back to read what people answer 
Hi, PFA-Goofy, I have already seen your answer, thanks a lot for that. I would take time to look at it, if i have questions, i would post below again. I really appreciate your effort.
np problem MIA6, glad if I could help.
Take your time, and come back if you have any more questions 
Take your time, and come back if you have any more questions
Hi everybody
Regarding cell differentiation, this only occur in the primative cells (stem cells), in which the cells divid and differentiate untill it become a mature cell performing the function that is designated to do.
Hope this can help