Final answer:
The antero-posterior axis of a chick is determined by genetically programmed dorsal cells and the arrangement of Hox genes, which map the body's anterior to posterior plan. Spemann and Mangold's experiments highlighted the influence of dorsal cells in axis formation, and further research on Hox genes has shown their pivotal role in maintaining body symmetry.
Step-by-step explanation:
Antero-Posterior Axis Formation in Chicks
The antero-posterior axis of a chick is determined mainly during embryonic development. Seminal experiments by Spemann and Mangold revealed that dorsal cells from one embryo, when transplanted into the belly region of another, led to the formation of a second notochord. This key discovery signified that the dorsal cells were genetically programmed to establish the body's axis. This axis, which specifies the head-to-tail direction, is an essential aspect of the chick's symmetry and overall body plan.
Axis formation is also influenced by the expression of Hox genes, which are arranged sequentially to map the anterior to posterior body plan. Mutations in these genes can result in loss of symmetry critical for the proper development of the organism. Therefore, the determination of the antero-posterior axis in a chick is a genetic process that occurs early in embryonic development.