Re: What is the importance of the regulation in the gene expression in human

In general, gene expression is the process by which the production of individual, genetically-encoded proteins is uniquely regulated in response to specific environmental and developmental signals.  Rather than attempt to re-write the textbooks, I'm going to refer you to some excellent online explanations of this broad & important topic.

Probably the best place to start is DNA from the Beginning: An Animated Primer on the Basics of DNA, Genes, and Heredity from the Cold Spring Harbor Laboratory.  The following chapters in particular focus on the principles of gene expression, including some useful examples:

The Molecular Biology of the Cell @ NCBI text is also a valuable resource for a more advanced discussion of gene expression.  The chapter entitled, Control of Gene Expression: An Overview of Gene Control, will probably be the most useful for you.  Click on the sub-headings in the orange "Outline" box on the left-hand side of the page to reach the individual sub-sections.  The section entitled, A Cell Can Change the Expression of Its Genes in Response to External Signals, contains some examples that you may find particularly helpful.

Regulated gene expression is crucial to the proper growth & survival of an organism and cannot be over-emphasized.  Without it, the genetic code of a chromosome is the equivalent of a computer data file without the appropriate application to run it.  In other words, the process of gene expression effectively translates a chromosomal nucleotide sequence into a functioning gene product.  I hope that these resources will help you to understand this extremely important process, which is the central principle of heredity.

Good luck,

Jeff