Atlas: epigenetic phenotypes

Developmental phenotypes can be extremely useful tools for investigating large scale changes to embryonic pattern. Common phenotypes include UV ventralization, lithium dorsalization and retinoic acid posteriorization. All of these phenotypes are variable. The dorso-anterior index (DAI) of Ken Kao and Rick Elinson (1988) can be used to grade the severity of the phenotype in each case.

DAI 0	DAI 1	DAI 2	DAI 3	DAI 4	DAI 5
No somites present; trace of tail mesenchyme occasionally seen.	No otic vesicle(s) present; somites present in trunk or portion thereof.	No visible retinal pigment; otic vesicles or single vesicle still visible.	Eyes fused or cyclopic, but at least some retinal pigment visible.	Reduced forehead; eyes smaller than normal and sometimes joined.	Normal.
DAI 10b	DAI 10a	DAI 9	DAI 8	DAI 7	DAI 6
Large proboscis.	Radial embryos with radial retinal pigment and cement gland. Substantial neural and notochordal tissue.	Multiple eyes and cement glands.	Completely lack a trunk, normal face (eyes sometimes enlarged). No obvious somites but can be detected with histology, notochord enlarged and irregularly shaped.	Severely reduced trunk, vestigial axis closely attached to head. Somites are visible in the short axis.	Slight bend in axis visible at stage 28.

These sketches are computer tracings of the original DAI images of Kao and Elinson (1988).