In conducting the study described in Problem 24, you have noted that a set of S. cerevisiae genes are repressed when yeast are grown under high-salt conditions. How might you approach this question if genome sequences for the related Saccharomyces species S. paradoxus, S. mikatae, and S. bayanus were also available?

How would you design a genetic screen to find genes involved in meiosis?

Substantial fractions of the genomes of many plants consist of segmental duplications; for example, approximately 40% of genes in the Arabidopsis genome are duplicated. How might you approach the functional characterization of such genes using reverse genetics?

A substantial fraction of almost every genome sequenced consists of genes that have no known function and that do not have sequence similarity to any genes with known function. How would your approach change if the genes of unknown function were in the human genome?

A substantial fraction of almost every genome sequenced consists of genes that have no known function and that do not have sequence similarity to any genes with known function. Describe two approaches to ascertaining the biological role of these genes in S. cerevisiae.

What is the difference between biochemical and biological function?

Using the two-hybrid system to detect interactions between proteins, you obtained the following results: A clone encoding gene A gave positive results with clones B and C; clone B gave positive results with clones A, D, and E but not C; and clone E gave positive results only with clone B. Another clone F gave positive results with clone G but not with any of A–E. Can you explain these results? To follow up your two-hybrid results, you isolate null loss-of-function mutations in each of the genes A–G. Mutants of genes A, B, C, D, and E grow at only 80% of the rate of the wild type, whereas mutants of genes F and G are phenotypically indistinguishable from the wild type. You construct several double-mutant strains: The ab, ac, ad, and ae double mutants all grow at about 80% of the rate of the wild type, but af and ag double mutants exhibit lethality. Explain these results. How do the two-hybrid system and genetic interaction results complement one another? Can you reconcile your two-hybrid system and genetic interaction results in a single model?

Mutations in the Drosophila Ultrabithorax (Ubx) gene result in wings developing from two thoracic segments, rather than just one as in wild-type flies. In the mouse genome there are two Ubx orthologs . How would you determine whether the two mouse genes have distinct or redundant functions?