Developmental Mechanisms
Introduction
These notes are intended to introduce a number of different mechanisms at the all levels that form structures within the embryo. These are general notes about these mechanisms giving only a few examples. For specific tissues and organs read the system notes.
What is remarkable, given our biological diversity, is the strong evolutionary conservation of these developmental mechanisms.
--Mark Hill 08:45, 15 May 2010 (EST) Currently template page only.
Axes
All embryos occupy 3 D space and appear differently externally and internally within this space. This gives us 3 different axes which need to be determined: Head/Tail (rostro/caudal), Front/Back (anterior/posterior), and Left/Right. The left/right axis appears at first mirror symetrical, and looks very similar externally, but clearly many internal organs are not duplicated (heart, liver, brain etc).
Cellular Mechanisms
These notes are intended to introduce a number of mechanisms at the cellular level that form structures within the embryo. These cellular dynamic and physical interactions form basic tissue structures of epithelia, connective tissues and features such as tubes.
Cell Migration
Molecular Mechanisms
This page is a link to many different resources related to Molecular Development. In current years we have turned from wanting to merely describe the events of embryogenesis, to a desire to understand the mechanisms of development. This has been a boon in allowing the use of many (easier) model systems such as the genetist's tool the fruitfly, and the worm, frog, chicken, zebrafish and mouse (see other embryos page).
A continuing theme also seems to be the reuse of signals at different times and places within the embryo, for diiferent jobs. This has given rise to the concept of "switches" which by themselves may contain no "information" but to activate other genes or switches. Finally, you can imagine that of our 20,000-25,000 protein-coding genes, a large number of these may only be expressed during development or if reused, have a completely different role in the mature animal.
Sex Determination
Eukaryotic organisms reproduce by generating haploid gamete cells, oocytes and spermatozoa, that in fertilization recombine to form the first diploid cell of the new organism. In normal human development, each gamete contains a single sex chromosome, the oocyte carries an X chromosome and the spermatozoa carries either an X or a Y chromosome. Initial sex determination is therefore determined by the spermatozoa and the specific sex chromosome it contains.
The term sex determination in development apples more broadly
Links: Genital System Development
Epigenetics
In terms of molecular mechanisms, the field of epigenetics has begun to florish with some recent important findings.
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2026, September 11) Embryology Developmental Mechanisms. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Developmental_Mechanisms
- © Dr Mark Hill 2026, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
