Significant depletion of serotonin and serotonin-derived metabolites; increase in exploration. Double mutant created by CRISPR-mediated deletion of 1450 bp spans Exon 1 to Exon 6 (the same deletion as syb3601 in PHX3601) in tph-1 background. Upstream flanking sequence: cctctgaaaaccaaatcttgttctctgaaa; Downstream flanking sequence: TCGCTGGTCTTCTTTCTTCTCGTGATTTCT.