Genetic dissection of vertebrate processes in the zebrafish: a comparison of uniparental and two-generation screens.

Genetic dissection is used to identify important genes in biological processes and is accomplished through the generation and study of mutations in model organisms. In diploid organisms, recessive mutations must be rendered hemizygous or homozygous for the mutant phenotype to be detected. In zebrafish (Danio rerio), this can be accomplished in two ways: (i) crosses between siblings who are potential carriers (in two-generation screens) and (ii) the generation of uniparental progeny. Two-generation screens have been the most productive to date but require substantial resources. However, uniparental screens involving haploids and half-tetrads (products of meiosis I) have also been productive, and require more modest resources. In genetic screens, the fraction of an average genome that is heterozygous (heterozygosity index) is inversely proportional to the likelihood that separate recessive mutations will be homozygous at the same time. Heterozygosity indices for haploid, half-tetrad, and two-generation screens are 0, 66, and 87.5%, respectively. Family sizes required to minimize bias in half-tetrad screens are also calculated. We conclude that gynogenetic half-tetrad screens are genetically robust and technically accessible to the independent researcher. The increasingly powerful genetic and experimental tools available for work with zebrafish can be used to address a broad range of questions in vertebrate biology.