Ift20 mutant mice embryos lack cilia production due to an absence of Arl13b expression. The embryo is significantly smaller than its wild-type counterparts and gets developmentally delayed at around the E8.5 stage. These mutants show no Nkx2.1 expression within the gut suggesting that the lung fails to develop without cilia. Ift88 mutants confirmed these same results. The Ift88 mutants showed that the gut can develop without cilia due to Hnf3b signals.