FMR1 and fragile X syndrome: These models have been genetically manipulated to emulate the genotype of FXS, knocking out or down the Fmr1 gene in mice and Drosophila. In both models, the olfactory system (OS) is the most conserved sensory system and critical for the species survival and reproduction, an ideal candidate to study sensory information processing issues found in the absence of FMRP.