Much is known about the genes that control trichome (hair) formation in Arabidopsis [Pattanaik et al., 2013]. At least 3 genes are required for normal trichome development. Plants without one of these genes simply don’t make trichomes. It’s a bit more complicated than I’m making it sound, but the plant needs glabrous-1 (GL1), glabrous-3 (GL3), and transparent-testa-glabra-1 (TTG1). Altogether, at least 70 genes are now known to play some role in influencing trichome development [Fambrini et al., 2019].