37. Cleavage
• Cleavage is a series of rapid mitotic divisions
whereby the enormous volume of egg cytoplasm
is divided into numerous smaller nucleated cells.
These cleavage stages are called blastomeres.
One consequence of this rapid division is that
the ratio to cytoplasmic to nuclear volume gets
increasingly smaller as cleavage progresses.
The rate of cell division and the placement of
blastomeres with respect to one another is
completely under the control of proteins and
mRNAs stored in the oocyte of the mother
65. fertilized egg of frog (cortical rotation)
if we allow rotation the larva is normal, if
rotation is inhibited with UVirradiation the
embryo is featureless and vetralized if we
treat the embryo with heavy water it will
enhance microtubule formation resulting into
the formation of cyclopean eye and over
developed sucker and if we impose second
rotation with centrifugation the result is
conjoined twin
84. Gastrulation
• It is the process of highly integrated cell
and tissue movements and their
rearrangements so as to develop a three
layered embryo composed of ectoderm,
mesoderm and endoderm.