When designing your transgenic construct, keep in mind that the transgene should be a complete transcriptional unit containing all elements required for gene expression. Once integrated, the transgene must be distinguishable from the endogenous gene and/or it's expressed products, and the entire transgenic fragment must be excised from the vector with as little vector sequences retained as possible.
The purified linear plasmid-based transgenic microinjection fragment should range in size from 2-25Kb and contain no more than 100bp vector sequences. Find out why.
BAC transgenic constructs range in size from 70-250Kb and can be injected in linearized or circular form. Integration rates are similar to smaller transgenes but fewer copies integrate. However, BAC transgenes are less susceptible to position effect variegation. Find out why.