Embryology

Embryology studies organisms as they develop before birth or hatching. It examines how fertilization, cell division, and differentiation produce an embryo and its structures.

Fertilization: The fusion of gametes that initiates development of a new organism. It usually begins embryonic development by combining parental genetic material.
Zygote: The single cell formed when two gametes fuse. It is the starting cell from which an embryo develops.
Congenital disorder: A structural or functional condition present at birth, arising before birth or during it. Developmental disruptions can produce congenital disorders.
Preformationism: The historical belief that a miniature organism exists within a gamete and merely enlarges during development. It opposed explanations in which embryonic form emerges through progressive development.
Spemann–Mangold organizer: An embryonic region that can induce surrounding tissue to form a secondary body axis. Its discovery showed that embryonic tissues can direct neighboring cells' development.
Cleavage: Rapid mitotic divisions of an early embryo, typically without overall growth. These divisions multiply cells soon after fertilization.
Blastocyst: An early mammalian embryo consisting of an inner cell mass and an outer trophoblast. Its structure precedes implantation and later embryonic development in mammals.
Prenatal diagnosis: Medical testing used to assess fetal health or detect conditions before birth. Developmental knowledge helps interpret findings about fetal structures and growth.
Epigenesis: The view that complex structures arise progressively during development from initially less differentiated material. Its account of newly formed structures challenged preformationist explanations.
Drosophila segmentation: The gene-regulated process that divides a fruit fly embryo into repeated body segments. It revealed how genes establish spatial patterns in an embryo.

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