Bilateral symmetry of the animal's body axis is present from the first cleavage, but the animal's cleavage pattern is radially symmetrical. Because of the concentration of yolk in the vegetal hemisphere the formation of the cleavage furrow in the yolk-containing ventral portion is slower and lags behind that in the animal hemisphere. EP-cadherin is important in adhesion between blastula cells. See Figure 5.10.
Cleavage occurs at oblique angles with daughter cells either moving to the right or to the left.
DD or Dd mother, all offspring had coils which opened on the right. The first two cleavage planes are meridianal. During cleavage, cytoplasm that will give rise to different parts of the embryo is segregated into different blastomeres. Cleavage in mammalian embryos is rotational, holoblastic, and asynchronous. Embryonic DNA is transcribed during cleavage.