Intraspecific regulatory variation due to cis and trans. Expression bias is the proportion of the difference between alleles: (allele1- allele2)/(allele1 + allele2). The parental mix is plotted on the x-axis and the F1 heterozygote is plotted on the y-axis. A 1:1 relationship would indicate 100% cis and a slope of zero would indicate 100% trans. A 1:1 line is shown for reference. The vast majority of the expression differences between the W lines and the tester line are attributed to cis, for the four genes and six lines tested (regression coefficient = 0.91 ± 0.13). Color code: line 84 - blue, line 181 - red, line 147 - purple, line 192 - orange, and line 68 - green.