(A) Probability of selecting embryos at interphase stages based on time following observation of the prior anaphase (see Materials and methods). Time-lapse movies of wild-type embryos (n = 23) were scored for timing of entry into mitotic metaphase. Metaphase entry times were assumed to be normally distributed, and a p-value indicating the likelihood of a staged embryo being within interphase were calculated for each of the indicated timepoints (x-axis). (B) Clustering of individual biological replicates. The total number of ‘open’ ATAC-seq fragments within the set of peaks associated with autosomes was calculated for each biological replicate. Correlation between samples (1-cor(samples)) was calculated and complete-linkage clustering was performed. Samples corresponding to metaphase NC11 (NC11_09, n = 3), metaphase NC12 (NC12_12, n = 4), and metaphase NC13 (NC13_18, n = 3) are color coded (dark red, red, and orange, respectively). (C) Detail of accessible chromatin profiles for each individual metaphase replicate over the hunchback locus. Coverage of ‘open’ ATAC-seq reads over the hunchback locus was plotted for each biological replicate of metaphase-staged embryos as indicated on the y-axis (CPM-normalized mean counts per 10 bp bin). Color coding is as in panel B. Genomic region plotted is as in Figure 1A, middle panel.