Since biochemical function is determined largely by specific enzymes (proteins), different sets of genes must be turned on and off in the various cell types. This is how cells differentiate.
The answer lies with what DNA is and how it works.
Since I’m assuming you know, all our DNA contains all of the information needed for making you. This information is stored in the over 20,000 human genes found in almost all our cells.
To get at the information, a gene must be turned on (expressed) and the information turned into something useful, a protein. Once made, that protein goes out into the cell and performs some set of specific tasks. For example, hemoglobin, a protein found in red blood cells, carries oxygen to cells and carbon dioxide away.
For a cell to work, 1000's of these proteins must be made, each doing its particular job. Our muscles and liver are so different because different sets of proteins are made in the various muscle and liver cells. In other words, in our muscles, genes are turned on for movement, but it also helps stabilize our joints, maintain our posture and generate heat during activity and the “detoxification" genes(liver cells) are off. In liver cells, the situation is reversed.
Genes are like Recipes for Proteins:-
Genes are recipes that provide instructions that make us who we are. They determine what we look like and help our body to grow and function properly.
