Figure 2.

How the frequencies and densities of SNP clusters vary with cluster size between the X chromosome and the autosomes, with simulated random data for comparison. Data series are: large white circles, simulated randomly occurring mutations; large black circles, the X chromosome; grey diamonds, mean value for the autosomes, calculated for each chromosome separately and then averaged. Error bars are one standard error of the mean. Simulated data are culled from 100 replicate simulations, accepting only those in which the terminal overall SNP density was one SNP every 1220 ± 100 bases, yielding approximately 40 runs. For full details of the simulations see §2. (a) How the frequencies of different cluster sizes vary; (b) how cluster density varies for the same data. At all but six cluster sizes above four, the X-chromosome density is lower than for the autosomes.