a, Strategy to block apoptotic cell competition and measure barrier function. b, Asymmetry score compares TEWL values from embryo’s left and right sides (n denotes number of embryos, F-test to compare variance). c, Experimental strategy for confetti lineage tracing. d, Representative whole-mount images of confetti-marked clones from each genotype at E17.5 (left, examples of clones from three litters of embryos analysed for each genotype). Examples of maximum projections and optical sections of individual epidermal layers are shown for each analysed fluorescent protein. SB, suprabasal. Right, quantification in wild-type embryos shows that approximately equal labelling efficiency is obtained at E17.5 with each of the three confetti fluorescent proteins (RFP n = 9 clones, YFP n = 11 clones, CFP n = 12 clones; Kruskal–Wallis test). e, f, Total clone size (e) and suprabasal clone size (f) dynamics for the genotypes indicated. All data are mean ± s.e.m. except for bar graphs, which show binned distributions.