The exons (and intervening small introns) that encode the mature robo2 protein have been replaced with a chimeric receptor (tagged with Tag:HA) containing the robo1 ectodomain and the robo2 cytoplasmic domain. The robo2KO.robo1-2 allele represents the loss of the robo2 open reading frame at the endogenous robo2 locus, while the robo1::robo21-2.robo2.HR.Tag:HA allele represents the chimeric receptor (tagged with Tag:HA) containing the robo1 ectodomain and the robo2 cytoplasmic domain that is expressed under the control of the robo2 regulatory sequences in place of robo2.
robo1::robo21-2.robo2.HR.Tag:HA, robo2KO.robo1-2 has viable phenotype
Fas2-positive longitudinal axons do not cross the midline in robo::lea1-2.lea.HR.T:Ivir\HA1 leaKO.robo1-2 double homozygous embryos (compared to crossing the midline in 23.7% of segments in lea null mutant embryos).