Question

Which of the following is the correct sequence of embryo development?
a. Cleavage, Gastrulation and Blastulation
b. Blastulation, Cleavage and Gastrulation
c. Cleavage, Blastulation and Gastrulation
d. Gastrulation, Blastulation and Cleavage

Answer 1

Hint: Embryonic development, known as embryogenesis, is the course by which the embryo forms and matures. In mammals, the term refers essentially to untimely stages of prenatal development, whereas the terms fetus and fetal development illustrate later stages. Embryonic development begins with the fertilization of the egg cell (ovum) by a sperm cell, (spermatozoon). Once fertilized, the ovum is called a zygote, a sole diploid cell.

Complete answer:
After fertilization, the growth of a multicellular organism proceeds by a method called cleavage, a series of mitotic divisions whereby the huge volume of egg cytoplasm is divided into plentiful smaller, nucleated cells. These cleavage-stage cells are known as blastomeres.

The cleavage results in the arrangement of an 8-16 cell structure called the morula. Blastulation is the creation of a blastula from a morula. Gastrulation is the route during embryonic development that transforms the embryo from a blastula with a solitary layer of cells to a gastrula possessing multiple layers of cells. Gastrulation characteristically involves the blastula folding in upon itself or dividing, which joins two layers of cells. The cavity of the gastrula is called the archenteron.

Hence, the correct answer is option (C).

Note: In amniotes, the cells of the morula are at primary closely aggregated, but almost immediately they get arranged into an outer or peripheral layer, the trophoblast, which does not give to the formation of the embryo proper, and an inner cell mass, from which the embryo is expanded. Fluid collects between the trophoblast and the better part of the inner cell mass, and thus the morula is renovated into a vesicle, called the blastodermic vesicle.