Lecture 2

Question 1

invagination

Answer 1

infolding of a sheet (epithelium) of cells, much like the indention of a soft rubber ball when it is poked

Question 2

involution

Answer 2

inward movement of an expanding outer layer so that it spreads over the internal surface of the remaining external cells

Question 3

ingression

Answer 3

migration of individual cells from the surface into the embryo’s interior. individual cells become mensechymal and migrate independently

Question 4

delamination

Answer 4

splitting of one cellular sheet into two or more or less parallel sheets. while on a cellular basis it resembles ingression, the results is the formation of a new (additional) epithelial sheet of cells

Question 5

epiboly

Answer 5

movement of epithelial sheets (usually ectodermal cells), spreading as a unit to enclose deeper layers of the embryo. can occur by cells dividing, by cells changing their shape, or by several layers of cells radially intercalculating into fewer layers; often all three mechanisms are used

Question 6

convergent extension

Answer 6

movement of more lateral cells of all germ layers toward the midline. this leads to a convergence of those cells causing their intercalation along the medial to lateral axis. as these cells converge en masse, the embryo extends along the anterior-to-posterior axis

Question 7

what diffeerentiates quail cells from chick cells

Answer 7

single large nucleus

Question 8

von baer’s laws of vertebrate embryology

Answer 8

1. the general features of a large group of animals appear earlier in development than do the specialized features of a smaller group
2. less general characters develop from the more general, until finally the most specialized appear
3. the embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them
4. therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo