N^Ax-59b homozygous clones always differentiate as epidermis when adjacent to wild type cells, all bristles along the border are wild type.

The Abruptex phenotype of heteroallelic combinations with viable Abruptex alleles is reduced at 29^oC as compared to 25^oC.

Neural precursors never form in the Ax class of N alleles. Cells mutant for Ax class alleles but with some neural potential are inhibited from becoming neural by their neighbours but do not themselves affect their neighbours, which can become neural. Homozygous mutant clones develop as epidermis, and this requires Dl function.

Clones in the thorax lack bristles.

Mutations of mam, bib and neur in an heterozygous condition had no effect on the expression of N^Ax-59d or N^Ax-59b except when coupled in cis with N^fa-g. The neurogenic mutations suppress the wing venation phenotype of N.

Heterozygotes lack the twin sensilla of the wing margin, and often lack the ventral sensillum of wing vein L3, the anterior cross vein sensillum and the three sensilla of wing vein L3.

Heterozygotes exhibit wing vein abnormalities.

Expression was suppressed by Dl mutations and enhanced by E(spl) and H mutations.

Developmental studies of Young have shown that N^Ax-59b is a pupal lethal (Kelley, Kidd, Deutsch and Young, 1987). Homozygotes and hemizygotes semi-lethal at 22^oC; lethality approximates 100% at 25^oC. Lethal in heterozygotes with N mutants but viable and fertile with recessive visibles at Notch. N^Ax-59b/N^Ax-59b; Dp(1;2)51b/+ are poorly viable and infertile and mutant phenotype is enhanced. N^Ax-59b/+; Dp(1;2)51b/+ females have diminished mutant expression compared to N^Ax-59b/+ females which in turn are similar to males Ax/Y; Dp(1;2)51b/+. In heterozygotes with spl at 25^oC, the eye is reduced in size but is larger than in spl/spl, and eye roughness varies from very mild to undetectable. The report by Welshons that N^Ax-59b/spl did not express the split phenotype was an error caused by uncontrolled temperature variation. In cis heterozygotes, spl N^Ax-59b/++, expression of split is enhanced compared to N^Ax-59b/spl; the eyes are rough and reduced in size. No such enhancement is seen when N^fa-g is coupled to N^Ax-59b and in N^Ax-59b/N^fa-g, the expression of the recessive is very mild and frequently nonpenetrant (Welshons, 1971). N^Ax-59b is semi-lethal with N^Ax-9 and lethal with alleles N^Ax-16, N^Ax-E2, N^Ax-71d, N^Ax-1 and the addition of Dp(1;2)51b to heterozygotes of N^Ax-59b with N^Ax-9 and N^Ax-1 restores viability (Portin, 1975). The temperature sensitivity of the N^Ax-59b phenotype is strongest at 25^oC; mutant expression decreases at both 18^oC and 29^oC, with the least mutant expression at 29^oC (Portin, 1981). At 18^oC, there is complementarity with all recessive visibles at Notch and strong Ax expression in every case except when heterozygous with N^fa-g. At 29^oC, all heterozygotes are noncomplementary with the exception of nd; Ax expression is diminished. At 29^oC, homozygotes or hemizygotes with Dp(1;2)51b are more viable than at 18^oC or 25^oC (Portin, 1977). At 25^oC, wing-vein interruption and bristle loss increases with an increased dose of the mutant gene (Portin, 1981). Somatic crossing over yields twin spots on cuticular surface of flies, indicating that N^Ax-59b is not a primary cell lethal (Portin, 1980). N^Ax-59b placed on the map of the Notch locus between spl and N^nd-2;