Neurons across the retina arraying in a non-random patterning are commonly referred as 'retinal mosaics'. This phenomenon indicates that each individual type of horizontal cells, amacrine cells and retinal ganglion cells are arranged in a regular array within their layer, covering the entire retina without dendritic overlapping and blind spot. Therefore, it theoretically assures that every type of retinal neuron functions on any single piece of retina. Recent researches point out that the formation of retinal mosaic involved several mechanisms including apoptosis. The balance of apoptosis and proliferation maintains the constant amount of retina neuron. Once the mice are overexpressed of anti-apoptotic gene bcl-2 or knock out of proapoptotic factor bax, the regularity of retinal mosaics would be disturbed in comparison of WT mouse retina. The neuron increased and clustered, showing the elimination of overcrowded cell in the normal developmental process. Coincidentally, in the dscam (Down's syndrome Cell Adhesion Molecules) knocked out mice, the same phenotype persists. Moreover, the dendrites of neighboring cell tangles together severely. Since the dscam is required in the neuron recognition and apoptosis, we hypothesize that dscam involved in the retina apoptotic pathway by homophilic interaction between the same cell types. To determine the influence of dscam on retina development, we overexpress normal and mutant version of DSCAM in the retina neuron. Following with TUNEL assay to examine the increasing apoptotic cells triggered by overexpressed dscam. This research could provide a further detail of the formation retinal mosaics.