In animal development, the process of cleavage produces a ball of cells with an interior cavity. In the succeeding evelopmental process, called gastrulation, the cells in the embryo migrate to form three layers of cells, the _______, _______, and _______, which in terms of location are the _______, _______, and ________ layers of cells in the organism.
The homeobox DNA sequence is said to be ____ because _____.
a. an induction sequence; it controls general development
b. highly unusual; it exists in only a few animals
c. a diversifying influence; it brings about differences in animals
d. fast-evolving; it changes every few generations
e. highly conserved; it has changed little over evolutionary time
The segregation of cells into different layers in development is strongly shaped by ______, while the transformation of the human hand from its webbed to its five-fingered form is strongly shaped by
a. morphogens; neural crest cells
b. cell adhesion; apoptosis
c. homeobox sequences; morphogens
d. apoptosis; cell adhesion
e. induction; neural crest cells