Coming from an engineering background I need to see the overall picture before getting bogged down in the details. I find it very hard to understand something if I can’t envisage it, therefore I try and break it in to simple pictures.
With the help of your explanation I now see the nucleus of the cell, (in my oversimplified terms as) as a transparent plastic bag full of water. Inside that plastic bag I have 46 pieces of soft cooked spaghetti of different lengths floating around. This spaghetti nucleus contains the story of the building instruction of the cell.
On the sides of these pieces of spaghetti a total story has been printed. The story is made up of 46 separate sentences. The story starts on spaghetti one, and like any good sentence the first letter is upper case to mark the start, the sentence then ends with a period to indicate the pause of the DNA. Then follows a postscript, which states the reader must go onto spaghetti two for the continuation of the story. Like any good story to read it one must start on sentence one and finish on the end of sentence 46.

Great, this simplistic vision is making sense to me, so the next thing that I do is to open that plastic bag and lay all the spaghetti in a straight line, end to end starting from spaghetti 1 and ending with spaghetti 46. In my mind this is now stretched out for 20 metres in front of me.

Now, the first thing that I start to look for in and story or set of building plans is an index. I would have though that by now science would have mapped some sort of plan on which DNA is doing what?

I am told that the human code contains 3,000,000,000 base pairs of DNA and that these base pairs make up the 25,000 different genes.

Right, now my next problem is what constitutes a gene?

I understand that each cell has 25,000 genes but each cell only uses a select few genes, how does it know what to use?

How would they know when one gene starts and ends, then the next one starts?

I am told that an embryo receives 25,000 genes from each parent, making a total of 50,000 genes, but as the child will only have 25,000 genes what happens to the others?

If Genes are made up of protein which is bonded amino acid, then by eating meat it would provides the protein the body requires, however eating plants does not provide any protein as the plants do not contain any. If that is true then how is the DNA of a plant bonded?

You will see from my questions that the problems I have is in understanding the overall concept of cells, not in the detail, well not yet, I have not got to those questions yet..

Regards Derek

The chromosomes are different sizes and some do contain more DNA than others.
The DNA string is not continuous from one chromosome to the next. A gene may be made up of a string of DNA found in a chromosome, but the same gene may be modified, controlled or activated by another set of DNA string (or genes) on some distance away in the same chromosome, or another chromosome.
So, the chromosomes are not specific to any set trait or function.
The genes are scattered throughout the genome and that’s why scientists are “looking” for genes (what they are and where they are located on the chromosomes) that control the different human traits.

My 3 question are;

Does this mean that this string of DNA instruction is not one continuous string but starts in one chromosome then is broken off and then continues again in the next chromosome. In other words it the one string divided into 46 separate parts?

Are the chromosomes all the same size, or do some contain more DNA than others?

Can the chromosomes then be broken up into some sort of very basic functions, example; Could chromosome 1 be responsible for the protein required for internal organs, chromosome 2 for growth and reproduction, etc etc?

Derek