4. Genes as carriers of information

Genes are not only carriers of inherited information but also they are extremely important instructors for embryological development. In the last decade there is a tremendous progress in identifying specific genes, which are responsible for control of development in human embryo. The earlier studies were initially performed in Drosophila and other laboratory animals have immensely contributed in understanding the pathways and genes involved in human development.

There are genes, which are involved in development of code for proteins, which include signaling molecules and receptors, DNA transcription factors, enzymes, transport systems and components of extracellular matrix. Thus mutations and defects in all of the mentioned factors above can lead to birth defects [3].

The genetic factors which initiate, maintain and establish embryonic development is not clearly determined yet. There are some key developmental pathways, which are identified after exhaustive experiments in genetic expression studies, but still the processes are not clear. The developmental gene families identified in vertebrates and mammals show sequence homology with developmental regulators of fruit fly Drosophila. The developmental genes produce proteins called transcription factors, which regulate RNA transcription from DNA template, by binding to regulatory DNA sequences to form complexes, which induces transcription by RNA polymerase. Thus gene expressions can be controlled by transcription factors thus in other words they can switch genes on and off. The variety of processes taking part during development include induction during which extracellular signals change fate of one type of cells to another, segmentation, migration, differentiation and apoptosis or programmed cell death. The protein signaling molecules identified to be involved in the above processes during development across specific belong to Transforming growth factor family, (TGF-beta), Wingless (Wnt) family and the Hedgehog (HH) family.
