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Yeast1

Schematic of creating a synthetic lethal double mutants. Two viable single deletion mutants (of different mating type) are crossed, and the haploid progeny undergo induced sporulation. are sorted to 4 different types depending on how the genome recombines. Figure from Tong, et al.

The majority of the single deletion mutants of the identified genes in the yeast genome are viable, which suggests redundancy in the some of their function. A way to identify some of the redundancies is to have a query gene deletion mutant that is viable, and crossing this with a large array of viable single deletion mutant of a different mating type. This mating produces haploid double mutants, which can then be used to screen for synthetic lethal double mutants. By using an automated robotic system, synthetic lethal double mutants can be identified in a high-throughput manner. http://www.ncbi.nlm.nih.gov/pubmed/11743205

Tong AHY, et al. (2001) Systematic genetic analysis with ordered arrays of yeast deletion mutants. Science 294(5550):2364-2368.

Tetrad dissection[[1]]Edit

Yeast1

96 well colonies after query deletion mutant was crossed with different single deletion mutants. A.Query deletion mutant crossed with an array of single deletion mutants. Spores from the synthetic lethal mutants that yield weak/sick colonies were then separated to determine the genotype of each type of spore. B. Tetrad analyses of certain synthetic lethal mutants. Spores can have a single double mutant, two double mutants, or none, depending on how the genetic recombination occurs. Note that a bni1.delta:bud6.delta double mutant haplotype is not lethal- rather, it produces a small colony, which suggests a diminished cellular function. Figure from Tong, et al.

This is a way to look at the genotypes of the different spores that could result from the mating of two different haploid cells. In nutrient-poor conditions, the newly formed diploid cell undergoes sporulation, where four haploid spores form. Depending on how the recombination occurs, there are four different ways in which the genome can rearrange. Tetrad (T) has a single double mutant spore, which is unable to form a colony. Non-parental ditype (NPD) spores have two types of spores, one of which are parental and the other is recombinant, which could yield two synthetic lethal mutants spores. Parental ditype (PD) have the same genotype as the parental generation, which lacks spores with the double deletion. Sorting the different types of haploid spores allows us to visualize viability of the organism after creating a double deletion.

ReferencesEdit

Tong AHY, et al. (2001) Systematic genetic analysis with ordered arrays of yeast deletion mutants. Science 294(5550):2364-2368.