In the case of ordinary transgenes, the expression region depends on the promoter. Transgenic mice expressing the whole body can be obtained by selecting promoters that express the whole body, such as Rosa26 and CAG. If you choose a promoter that expresses certain tissue-specific genes, you will get transgenic mice that are expressed in a tissue-specific manner, such as AP2 and I will. This transgenic strategy is to inject transgenic fragments directly into fertilized mouse eggs.
Transgenic fragments are randomly inserted into the mouse genome because they are completely random and can be inserted. Some inhibitory regions cause the introduced genes to not express, and some enhancement regions can also be inserted to cause high expression of the introduced genes. The first generation of transgenic mice obtained by injection of prokaryotes is called the founder. Due to the randomness mentioned above, the founder is different, and the strain derived from each founder is called the strain. The expression may vary from row to row.