Vertebrate Embryology
The phylotypic stage is the stage at which all vertebrates resemble one another. Hence, it is the stage at which chick and mouse embryos are most similar morphologically. In this phase of development, the template bodies of the vertebrates are being laid down and certain biochemical signals – epigenetic changes - decides the fate of early embryo’s cells (Richardson, 903). It resembles the organogenetic period when many organ primordia that are undifferentiated are beginning to appear. Various peculiarities make it hard to clearly point out a well-defined phylotypic vertebrate development phase among all these species (Irie and Atsuko, 1).
Firstly, the developing organs of the vertebrate organs do not appear in synchrony but appears to have a progressive development from the head to tail. Secondly, the level of developmental autonomy indicates that the developmental primordial in a specific species develops is in synch with other species of the vertebrates. This blurs the various landmarks that can be used in staging, and even makes it hard to compare the various stages between these species (Richardson, 903). . The similarities would make it difficult for an individual to differentiate between the embryo of a mouse and a chick at this particular stage of development.
At the earliest stages of development, embryos have some specific differences that relates to the body size, body plan, the pattern of growth and development timing. This could be due to the notion that the eggs of various vertebrates are different. As such, the early cleavage embryos of various vertebrates such as chickens and mouse are different because of the limitations that the large chicken yolk imposes (Luskin,1). This means that the body size, growth pattern and the timing of the chick will be different from that of a mouse.
References
Irie, Naoki, and Atsuko Sehara-Fujisawa. "The vertebrate phylotypic stage and an early bilaterian-related stage in mouse embryogenesis defined by genomic information." BMC biology 5.1 (2007): 1.
Richardson, Michael K. "A phylotypic stage for all animals?." Developmental cell 22.5 (2012): 903-904.
Luskin, Casey. "Biology Textbooks Misuse Embryology to Argue for Evolution." 1
