Lec 1 (Historical perspective & milestones)

By careful observations of chick embryos it was found that the egg acquired its form over time (not pre formed), who discovered this?

Aristotle

Oviparity

birth from eggs

Viviparity

Live birth

Ovoviviparity

Production of an egg that hatches inside the body

Holoblastic cell division

cleavage where the entire egg is divided into successively smaller cells

• frogs, salamanders

Meroblastic cell division

cleavage where only part of the egg is destined to become the embryo, while the other portion (yolk) serves as nutrition for the embryo

What is Aristotle’s theory of epigenesis?

Organs develop gradually in the embryo and are no preformed

Who depicted a human uterus opened to reveal the foetus and associated membranes

Leonardo da Vinci

Foetus

A fetus or foetus is the unborn offspring of a viviparous animal that develops from an embryo

Who made many illustrations of embryos and foetuses at different stages of development?

Hieronymus Fabricius

Who published illustrations of canine and ovine embryos in 1552?

Bartolomeo Eustachius

Prior to the preformation theory there was? What did it apply to?

Spontaneous generation of animals

• only applied to “lower” animals (flies)

Ovism model

location of preformed parts in egg

Spermism model

location of preformed parts in sperm

“Ontogeny recapitulates phylogeny” Who said this? And why is it incorrect?

Ernst Haeckel: embryos of ‘higher’ animals pass through stages that resemble the adult forms of their evolutionary ancestors

• outdated, higher & lower animals not relative as every organism is evolved to full capacity

• modern biology emphasizes the complexity of evolutionary processes

How did Wilhelm His contribute to the study of Developmental Biology?

• contributions to embryology and the study of brain, muscle and heart development

• cell tracing techniques: origin of tissues and organs and differentiation

How did Hans Spemann contribute to the study of Developmental Biology?

• Nobel prize

• Early amphibian “organizer” region in gastrulation

• Induction events of transplanted tissue

• Autonomous versus conditional specification