In order to provide a good minigene model, the gene fragment should have all of the necessary elements to ensure it exhibits the same alternative splicing (AS) patterns as the wild type gene, i.e., the length of the fragment must include all upstream and downstream sequences which can affect its splicing. Therefore, most minigene designs begin with a thorough in silico analysis of the requirements of the experiment before any "wet" lab work is conducted. With the advent of Bioinformatics and widespread use of computers, several good programs now exist for the identification of cis-acting control regions that affect the splicing outcomes of a gene  and advanced programs can even consider splicing outcomes in various tissue types. Differences in minigenes are usually reflected in the final size of the fragment, which is in turn a reflection of the complexity of the minigene itself. The number of foreign DNA elements (exon and introns) inserted into the constitutive exons and introns of a given fragment varies with the type of experiment and the information being sought. A typical experiment might involve wild type minigenes which are expected to express genes normally in a comparison run against genetically engineered allelic variations which replace the wild-type gene and have been cloned into the same flanking sequences as the original fragment. These types of experiments help to determine the effect of various mutations on pre-mRNA splicing.