How do mammals, including humans, solve the "dosage problem" caused by the presence of an x and y chromosome in one sex and two x chromosomes in the other sex? a. they don't; the fact that females have twice as much x chromosome protein products as males is critical for sex determination in mammals. b. females produce twice the rna transcripts as males do, but in females half of them are destroyed before being translated. c. in males, the x chromosome is up-regulated so that its genes are transcribed and translated twice as much as the x chromosomes in females. d. in females, one of the x chromosomes is condensed and largely inactive so that each sex has one active x chromosome. e. male rna transcripts from the x chromosome have leaders that cause them to be translated at twice the rate as those in females. f. they don't, but the x chromosome contains genes whose expression is not quantitatively sensitive, so the differences are not important.