The zygote passes through several developmental stages till implantation, Describe each stage briefly with suitable diagrams.
The following figure shows various stages of zygote development till implantation:
(a) The zygote divides into two-cell stage called cleavage. This development takes place when the zygote is still in the isthmus.
(b) The cleavage undergoes further rounds of mitosis to form 2, 4, 8 and finally 16-celled stage.
These daughter cells are called blastomere.
(c) The 16-celled stage is known as morula.
(d) The morula changes into blastocyst; with more rounds of meiosis. At this stage, the blastomeres are arranged in an outer layer of cells; called trophoblast and an inner mass of cells.
(e) Implantation to uterine wall happens at the blastocyst stage.