All of the cells within a complex multi-cellular organism such as a human being contain the same DNA; however, the body of such an organism is clearly composed of many different types of cells.
What, then, makes a liver cell different from a skin or muscle cell is the way each cell deploy (utilizes) its genome. In other words, the particular combination of genes that are turned on (expressed) or turned off (repressed) dictates cellular morphology (shape) and function. This process of gene expression is regulated by cues from both within and outside cells, and the interplay between these cues and the genome affects essentially all processes that occur during embryonic development and adult life.
Outside/Environmental cues include small molecules, secreted proteins (growth factors or signaling molecules), temperature, and oxygen.
The signaling molecules trigger intercellular signaling cascades (series of chemical reactions) that ultimately cause semipermanent changes in expression of genes. Such changes in gene expression can include turning genes completely on or off.
This process is thought to regulate a vast number of cell behaviors, including cell fate decisions during embryogenesis, cell function, and chemotaxis (i.e. cell movement in response to concentration gradient of a particular substance.)
this website is for anybody really not just for girls just saying, also while a lot of males are mean and you know there are the few who are kind and then there's the nice-guys but then theirs also guys like me who are shy we don't get out much because there are people like you who exist who would most likely punch a guy in the face so next time just think about things before you post them to a website where guys and girls can see your question.