Clonal Analysis with Genetic Mosaics

Most loss-of-function mutations are recessive, thus showing phenotypes in homozygous mutant organisms. A significant fraction of these mutations affect developmental processes, causing lethality. Analysis of lethal mutations is complicated since homozygous mutants die during development. This chapter discusses making genetic mosaics to study the function of such essential genes. The mosaic analysis is invaluable for analyzing the function of essential genes. We will review various methods for making mosaic clones using mitotic recombinationrecombinationmitotic induced by irradiation or the FLP-FRTFLP-FRT technique in Drosophila. Mosaic analysis with a repressible cell marker (MARCM)MARCM further extends the FLP-FRT techniques to mark the mutant clones for cell lineage analysis. We will also discuss mosaic analysis with double markers (MADM), a modified version of MARCM developed for mosaic analysismosaic analysis in mice. We will cover germline clonal analysis for maternal genesmaternal gene crucial for early embryo development before the onset of zygotic gene expression. Lastly, we shall discuss how clonal analysis led to the finding of the selector gene function in the compartmentalization of developing organs.