Embryology

Embryology is the branch of developmental biology that studies embryos and their development. It is also used to support the validity of the theory of evolution. Embryology is the classic study of morphological changes within the embryo. Aristotle is described as the first one to do such study, braking chick eggs after different hours of incubation and observing the ontogeny of the chicken structures. After 50´s, with the DNA structure being created by Watson and Crick, and the increasing knowledge in molecular biology field, developmental biology emerged as the field of study that correlates the genes and such morphological changes; in order words, which genes are responsible for each morphological change that takes place in an embryo. More than explain those morphological changes, to explain how the many different cell types of a multicellular organism arise from the single fertilized cell, the egg, is another aim of developmental biology. For more details, it is recomended the following readings: Developmental Biology; Scott F Gilbert, and Principles of Development; Lewis Wolpert.

Ontogeny

Ontogeny (also ontogenesis or morphogenesis) describes the origin and the development of an organism from the fertilized egg to its mature form. Ontogeny is studied in developmental biology.

The idea that ontogeny recapitulates phylogeny, that is, that the development of an organism exactly mirrors the evolutionary development of the species, is discredited today. However the phenomenon of recapitulation, in which a developing organism will for a time show a similar trait or attribute to that of an ancestral species, only to have it disappear at a later stage is well documented. For example, embryos of the baleen whale still develop teeth at certain embryonic stages, only to later disappear. A more general example is the emergence of pharyngeal gill pouches of lower vertebrates in almost all mammalian embryos at early stages of development. (April, 2001)

References

ISBN links support NWE through referral fees

• UNSW Embryology Huge resource of information and media

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