Genetics and the environment both play roles in cell differentiation. which is the best example of an environmental factor? the cells of a chicken embryo divide to form three layers: the ectoderm, mesoderm, and endoderm during meiosis, a single cell divides to form four gametes with half the number of chromosomes that somatic cells have. the terminal bud on a runner of a strawberry plant begins growing roots when it contacts the ground. cambium cells in the trunk of an apple tree form rings of xylem and phloem annually.