Dscam1²³/Dscam1²¹ transheterozygous embryos show defects in dendritogenesis in the embryonic aCC motoneurons (misplacement of primary branches) compared to controls. No gross morphology defects are observed in the MP1 neurons at early embryonic stage.

Mutants show increased overlap and fasciculation of self-dendrites among dendritic arborization neurons in the larval body wall.

In Dscam^R496W/Dscam²³ flies, the dorsal lobe nerve tract of the mushroom body does not form and the the medial lobe fails to extend to the midline. These phenotypes are 100% penetrant and exhibit similar but slightly weaker expressivity than Dscam²³.

100% of Dscam^FRT/Dscam²³ animals survive to late pupal stages.

Less than 25% of Dscam²¹/Dscam²³ or Dscam^Df6055/Dscam²³ larvae survive to late pupal stages.

Over 75% of Dscam^3.31.8/Dscam²³, Dscam^10.27.25/Dscam²³ and Dscam^6.5.9/Dscam²³ animals survive to late pupal stages.

Dscam²¹/Dscam²³ embryos show defects in the organisation of the central nervous system, showing severely disrupted longitudinal tracts and some aberrant midline crossing.

Dscam^3.31.8/Dscam²³, Dscam^10.27.25/Dscam²³ and Dscam^6.5.9/Dscam²³ embryos show defects in the organisation of the central nervous system, showing disrupted longitudinal tracts.

Class I da neurons show defects in self-avoidance in Dscam²¹/Dscam²³ larvae, such that in contrast to wild type, class I dendrites from the same cell overlap extensively and fasciculate in the mutant animals. Arbors of each cell project to the same general location as in wild type, but there are significant gaps in territory coverage.

Individual ddaD neurons of Dscam²³/Dscam⁴⁷ larvae show significant dendrite crossing, indicating defects in self-avoidance.

Single cell homozygous da neuron clones show defects in self-avoidance, with dendrites of the single cell overlapping extensively. These defects are seen in single cell clones of class I da neurons (such as ddaD), class II da neurons (such as ldaA), class III da neurons (such as ddaA) and class IV da neurons (such as ddaC). Targeting is grossly normal in these mutant clones, with two exceptions; in several clones, main dendritic trunks fail to properly segregate, leaving some regions of the body wall devoid of dendrites, and dendrites in the lateral regions of the body wall (from ldaB, ddaA and ldaA) form dense accumulations near the lateral chordotonal organ.

Class IV da neurons in Dscam²¹/Dscam²³ larvae show self-avoidance defects, but the tiling pattern is not obviously disrupted compared to wild type.

Small clones of Dscam²¹ cells induced in the mushroom body at the early third instar and then examined 24-36 hours later are often seen as multiple fascicles (in contrast to wild-type control clones which form single fascicles). Defects in branching are also seen in the mushroom body lobes; the mutant clones still form two distinct branches, but often the branches fail to segregate dorsally and medially.

Or47a-expressing olfactory receptor neurons (ORNs) that are mutant for Dscam²³ show marked mis-targeting of axons in the antennal lobe as they project towards wild-type targets (glomerulus DM3) on the ipsilateral side. The penetrance of the mistargeting phenotype is 100% with variable expressivity (on average about half of the mutant axons terminate in their correct glomerulus). P{GAL4}GH298-expressing ORNs that are mutant for Dscam²³ often fail to project to their normal target (the V glomerulus). In about 50% of cases, mutant axons leave the nerve, turn ventrally as in wild type and innervate ectopic positions within the ventral region of the antennal lobe. In the remaining cases the mutant axons do not turn ventrally and terminate more dorsally, typically in more central and lateral regions of the lobe. Or22a-expressing and Or23a-expressing Dscam²³ mutant ORNs target normally to the correct glomerulus. Or47b-expressing Dscam²³ mutant ORNs show mistargeting to more dorsal regions of the antennal lobe than the normal target (the VA1 l/m glomerulus) and also targeting defects in the contralateral lobe. Or46a-expressing Dscam²³ mutant ORNs frequently terminate upon entering the ventral central nervous system before reaching the antennal lobe, either immediately prior to entering the suboesophageal ganglion or upon exiting it, just ventral to the antennal lobe. The mutant ORNs form a structure with the appearance of a glomerulus where they terminate.