Table 5. Fixed parameters with references justifying values used.

Parameter	Description	Value	Justification
$N$	Number of histones	60	Berry et al., 2017a
$k_{\text{me0-1}}$	PRC2-mediated methylation rate (me0 to me1) (histone−1 s−1)	$9k_{\text{me}}$
$k_{\text{me1-2}}$	PRC2-mediated methylation rate (me1 to me2) (histone−1 s−1)	$6k_{\text{me}}$
$k_{\text{me2-3}}$	PRC2-mediated methylation rate (me2 to me3) (histone−1 s−1)	$k_{\text{me}}$
${\gamma }_{\text{me2-3}}$	Noisy methylation rate (me2 to me3) (histone−1 s−1)	$k_{\text{me2-3}}/20$
${\gamma }_{\text{me1-2}}$	Noisy methylation rate (me1 to me2) (histone−1 s−1)	$k_{\text{me1-2}}/20$
${\gamma }_{\text{me0-1}}$	Noisy methylation rate (me0 to me1) (histone−1 s−1)	$k_{\text{me0-1}}/20$
$\beta$	Relative local PRC2-activity	1
${\rho }_{\text{me2}}$	Relative activation of PRC2 by H3K27me2	0.1
${\gamma }_{dem}$	Noisy demethylation rate (histone−1 s−1)	$f_{min}{p}_{dem}$
$f_{lim}$	Limit on maximum transcription initiation (s−1)	1/60
PT	Threshold for full repression of transcription	1/3	Hepworth et al., 2018; Jadhav et al., 2020
$f_{min}$	Minimum transcription initiation rate (s−1)	$f_{max}/25$	Yang et al., 2014
$f_{max}$	Maximum transcription initiation rate (s−1)	${7.5\bullet 10}^{-4}$	Yang et al., 2014; Ietswaart et al., 2017
$p_{dem}$	Demethylation probability (histone−1 transcription−1)	0.17	Figure 2—figure supplement 2
$p_{ex}$	Histone exchange probability (histone−1 transcription−1)	${8.3\bullet 10}^{-2}$
$c_w$	Cell cycle length in warm (22°C) conditions (h)	22	Rahni and Birnbaum, 2019; Zhao et al., 2020
$c_c$	Cell cycle length in cold (5°C) conditions (h)	154