The Molecules That Are "Switched On" After Fertilization And Begin Sculpting Arms, Fingers, Vertebrae, Ribs, A Brain, And Other Body Parts Are Called?

I believe they are known as "master control genes" and develop the foetus in areas such as head, arms, legs, digestive systems, and their organs' many shape's and sizes, etc. An enzyme known as hedgehog is responsible for activating these genes and their development. However, this is rather old information (a documentary around 6 years ago), so you may want to research the above terms independently to get a more modern overview of the subject... Genes are fascinating!

Take care
Penfold