The study of a process of progressive changes through which a fertilized egg passes before it assumes an adult form is :

Explanation

The study of a process of progressive changes through which a fertilized egg passes before it assumes an adult form is embryology. Embryology is the branch of biology that focuses on the study of the development and formation of embryos and fetuses, especially during the early stages of development. It is a subfield of developmental biology and encompasses a wide range of research and study areas related to how organisms grow and develop from a single cell into a complex multicellular organism. Many studies in embryology use model organisms, such as fruit flies (Drosophila), frogs (Xenopus), and mice (Mus musculus), to understand developmental processes and genetics.