External views of mouse embryos after 10.5 days of embryonic development. The embryos on the left show a technique for revealing where individual genes are expressed (Wnt1, Wnt5a and Wnt11). The middle panel shows the mapping of three gene expression patterns as indicated. On the right, the patterns of all 19 Wnt encoding genes are shown, each in a different colour. The embryo space is mapped out by the different expression patterns of these genes, each vital for normal development; a mutation in any one gene can be lethal.