The development of transgenic technology during recent years has allowed researchers to probe much more deeply than was previously possible into the molecular mechanisms influencing embryonic development. Transgenic procedures allow the transfer of a cloned gene into a host genome or the mutation of specific genomic sequences via targeting in embryonic stem (ES) cells (seeChapter 7 ). Most commonly, transgenic gene transfer experiments have been used to study the phenotypic effects caused by the misexpression or overexpression of a transgene (1 –3 ), or to investigate the transcriptional mechanisms underlying developmental and tissue-specific gene regulation (4 –6 ). The use of reporter genes in this latter application will be dealt with in this chapter.
