Gene expression variation in African and European populations of Drosophila melanogaster

Table 3 Expression polymorphism on the X chromosome and autosomes

	X chromosome	Autosomes	X/A ratio*
Number and percentage of polymorphic probes
Overall	335 (35.8%)	1,559 (37.9%)	0.945 (P = 0.22)
Europe	155 (16.5%)	809 (19.7%)	0.838 (P = 0.027)
Africa	168 (17.9%)	871 (21.2%)	0.844 (P = 0.025)
Between	277 (29.6%)	1,323 (32.2%)	0.919 (P = 0.12)
Average percentage of pairwise differences
Overall	2.02	2.90	0.697 (P = 0.040)
Europe	1.77	2.68	0.661 (P = 0.014)
Africa	1.86	2.64	0.705 (P = 0.017)
Between	2.20	3.11	0.708 (P = 0.035)

*Deviations from 1:1 expectations for the X/A ratios were tested with two-tailed Fisher's exact tests for the percentage of polymorphic genes and with Mann-Whitney U tests for the average number of pairwise differences.

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