Developmental Biology has been one of the most exciting areas of biological research since the 1980s, with advances from three main concepts: Experimental Embryology, Developmental Genetics, and Molecular Biology.
Experimental embryology, which focuses on Embryonic Induction, flourished in the late 1970s when mass genetic screens were carried out on the fruitfly and thousands of mutations were examined.
Developmental genetics, which identifies a high proportion of the genes that control development, not just in Drosophila, but in all animals, flourished in the late 1970s.
Other technologies such as artificial insemination by donor (AID), egg donation, cryopreservation, embryo transfer, and the science of teratology study the effects of environmental agents such as chemicals, viral infection, or radiation on embryos.
Exceptions to genomic equivalence include antibody forming genes of B lymphocytes and the T-cell receptor genes of T lymphocytes, which undergo rearrangement at the DNA level, and certain nematodes, which shed chromosomes from some cell lineages during development.
Blastula, the cells are being bound by cadherins, and will usually have a system of tight junctions forming a seal between the external environment and the internal environment of the blastocoel.
If the animal and vegetal poles are at the top and bottom, then the equatorial plane is the horizontal plane dividing the egg into animal and vegetal hemispheres.
The terms proximal and distal are usually used in relation to appendages, proximal meaning “near the body” and distal meaning “ further away from the body.”