A biology graduate student presented a seminar where he described an experiment in which two closely related Drosophila species have been crossed. Both parental species and the F1 generation have been studied using RNA-seq. For reads with single nucleotide polymorphisms (SNPs) between the two species, he could determine from which allele they had been transcribed. He was interested in finding genes with differential expression levels between species caused by trans-acting mutations. Which genes should he select