cis versus trans effects

Emerson JJ, Hsieh L-H, Sung H-M, Wang T-Y, Huang C-J, Lu HH-S, Lu M-YJ, Wu S-H & Li W-H 2010 Natural selection on cis and trans regulation in yeasts. Genome Res 20:826-836.

• expression polymorphism in yeast is common for both cis and trans
• though trans variation is more common
• both cis and trans polymorphism are clearly under purifying selection
• though trans variation appears to be more sensitive to selective constraint
• cis divergence is more frequently mediated by positive Darwinian selection than is trans divergence

• studies in Drosophila took advantage of comparing the allele-specific expression (ASE) patterns of two parental strains to that of their hybrid offspring (i.e., F₁ hybrids) to investigate cis and trans expression evolution (Wittkopp et al. 2004, 2008)
• this experimental design measures the combined expression variation (both cis and trans effects) at a locus through measurement of expression differences between two parental strains
• expression differences measured within the F₁ hybrids between the same two strains can no longer be attributed to trans-factors
• as both genomes share the same cell and the same trans-factors
• consequently, the hybrid experiment measures only cis variation