Activity map of the tammar X chromosome shows that marsupial X inactivation is incomplete and escape is stochastic

Table 2 Quantitative analysis of female fibroblast RNA-FISH data

Frequency of nuclei with 2, 1 or 0 signals for each X-borne locus. At least 100 nuclei were scored. Only nuclei with two signals for the autosomal control gene, and therefore diploid, were scored. Male efficiencies were used to calculate the expected frequency of nuclei with two signals, one signal and no signal for each test gene. Expected frequencies of cells with two signals were in excess of 90% for all loci, and observed frequencies were significantly different from these expected frequencies in every case (Chi-square test with 2 degrees of freedom). Genes highlighted in bold were used in sequential RNA-DNA FISH experiments.

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