Question

what is the difference between:

1. the ingression of cells in the chick versus the involution of cells in the frog.

2. the movement of Hansen's node in the chick versus the lack of movement in the blastopore.

Answer 1

1.Ingression of cells in the chick-Developmental fates of cells emigrating from the primitive streak were traced by a fluorescent dye Dil both in chick and in quail embryos from the fully grown streak stage to 12 somite stage,focusing on the develooment of mesoderm and especially on the timing of ingression of each level of somitic mesoderm.The fate maps of the chick and quail streak were alike,although the chick streak was longer at all stages examined.

Involution of cells in the frog-The process of gastrulation is a continuous activity succeeding,cleav-age.during this process the blastodermal cells begin to move.they wander and occupy their prospective organ forming zones.during this movsment at one region on the blastula,the cells wander inside and occupy the blastocoelic cavity.

Difference between ingression and involution-

Ingression-During ingression,cells leave an epithellial sheet by transforming from well behaved epithellial cells into freely migrating mesenchyme cells.

Involution- During involution,a tissue sheet rolls inward to form an underlying layer via bulk movement of tissue.

2.Movement of hansen node in chick-In vertebrates,the readily apparent left-right anatomical asymmetries of the internal organs can be traced to molecular events initiated at or near the time of gastrulation.However,the earliest steps of this process do not seem to be universally conserved.It is the relative displacement of cells that is responsible for establishing their assymetric expression patterns.

Lack of movement in blastopore-Blastopore,the opening by which the cavity of the gastrula,an embryonic stage in animal development.

Most cells of the animal body are motile,and in the devdloping embryo their movements are often expensive,dramatic and syrprising.Controlled changes of gene expression create ordered arrays of cells in different states.cell movements rearrange these cellular building blocks and put them in proper places.the genes that the cells express determine how they move,in the sense,the control of gene expression is the primary phenomenon.