Part of intraflagellar transport (IFT) particles involved in ciliary process assembly. May play a role in the trafficking of ciliary membrane proteins from the Golgi complex to the cilium (PubMed:16775004). Regulates the ciliary platelet-derived growth factor receptor-alpha (PDGFRA) signaling pathway. Required for protein stability of E3 ubiquitin ligases CBL and CBLB that mediate ubiquitination and internalization of PDGFRA for proper feedback inhibition of PDGFRA signaling (PubMed:29237719). Essential for male fertility. Plays an important role in spermatogenesis, particularly spermiogenesis, when germ cells form flagella. May play a role in the transport of flagellar proteins ODF2 and SPAG16 to build sperm flagella and in the removal of redundant sperm cytoplasm (PubMed:27682589). Also involved in autophagy since it is required for trafficking of ATG16L and the expansion of the autophagic compartment (PubMed:24089209). Component of the IFT complex B, at least composed of IFT20, IFT22, HSPB11/IFT25, IFT27, IFT46, IFT52, TRAF3IP1/IFT54, IFT57, IFT74, IFT80, IFT81, and IFT88 (PubMed:12821668, PubMed:16775004, PubMed:19253336). Interacts directly with IFT57 and KIF3B/Kinesin II subunit (PubMed:12821668). Interacts with IFT88 (PubMed:19253336). Interacts with CEP83 (By similarity). Interacts with SPEF2 (via C-terminus) (PubMed:19889948). Interacts with CBL and CBLB (By similarity). Interacts with TRIP11 (PubMed:19112494). Interacts with TTC21A (By similarity). Interacts with SPATA1 (PubMed:31816150). Interacts with USH1G (By similarity). Present at the centrosomes during the cell cycle and associated with the proximal portion of the mother centriole and the lateral aspect of the daughter centriole (PubMed:15337773). Associated with basal body at the base of primary cilia (PubMed:15337773). Detected in the Golgi apparatus of round spermatids and late spermatocytes (PubMed:19889948, PubMed:28619825). Also detected in the manchette of step 10-12 spermatids (PubMed:19889948, PubMed:28619825). In step 14 spermatids, found in the basal body of the sperm tail (PubMed:19889948). Localization in the manchette of elongating spermatids is dependent on SPAG17 (PubMed:29690537). Expressed predominantly in the testis (at protein level). Expressed in kidney and retina. Expression is up-regulated during spermiogenesis. Expression is first detected at postnatal day 16 (P16) and increases significantly at days P30 and P42. Conditional knockout in male germ cells results in infertility, abnormal sperm morphology, significantly reduced sperm count and sperm mobility. Cells that stably express short interference RNAs targeting IFT20 show reduced centriolar IFT20 and lack primary cilia.