One method of analyzing gene function is to examine phenotypes of tissue homozygous mutant for a gene of interest. A problem with this approach is that the wildtype gene product is often essential for an organism to develop to a stage where the tissue can be examined. A solution is to generate clones of homozygous mutant cells in animals that are otherwise heterozygous. Clones are generated by first recombining a mutation onto a chromosome that contains a Flippase Recombination Target (FRT) sequence. Expression of Flippase in animals heterozygous for the chromosome and a wildtype FRT chromosome results in recombination and daughter cells that are either homozygous for the mutation or for the wildtype chromosome.This is particularly useful when analyzing the maternal effect of homozygous lethal mutations in Drosophila melanogaster as female germline cells can be made homozygous for the mutation while somatic cells are heterozygous for the mutation and thus the organism is viable. For easy selection of germline clones, the dominant female sterile mutation, ovoD,is used as only recombined cells that are homozygous for the mutation develop successfully. Currently, a chromosome with FRT 42D and ovoD is not available. I have created this chromosome and am using it to analyze the maternal effect phenotype of 237 P-transposable element induced lethal mutations from the Drosophila Stock Center at Bloomington, Indiana that were each recombined onto chromosomes with FRT 42D.