Final answer:
The absence of Cerberus, Nodal, or Pitx2 genes in embryonic development results in defective left-right asymmetry, impacting body axes positioning and cell differentiation.
Step-by-step explanation:
The question relates to embryonic development and the effects of the absence of certain genes, specifically Cerberus, Nodal, or Pitx2. These genes are involved in the establishment of the left-right asymmetry during embryogenesis. When these genes are not present, the usual result is a defective left-right asymmetry, which can lead to various developmental disorders due to improper positioning and differentiation of body axes and cell layers.
Interstitially, Cerberus, Nodal, and Pitx2 act as molecular signals that guide the developmental process of symmetry in the early stages of an embryo's life. Their absence means that the zygote may not establish a clear dorsal-ventral or anterior-posterior axis, leading to significant deviations in morphology and organ positioning.