What is the correct sequence of mammalian development stages?

The correct sequence of mammalian development stages starts with the formation of the zygote, which is the result of the fusion of the sperm and egg during fertilization. This single-cell zygote undergoes rapid cell division and cleavage, leading to the morula stage, which is a solid ball of cells.

As cell division continues and the morula develops, it transforms into the blastocyst, a hollow structure that includes an inner cell mass (which will eventually form the embryo) and an outer layer of cells (trophoblast) that will contribute to the placenta. After implantation into the uterine wall, the blastocyst undergoes further differentiation and development into the gastrula stage. The gastrula is characterized by the establishment of the three germ layers: ectoderm, mesoderm, and endoderm, which will give rise to all the tissues and organs in the developing fetus.

In the final stage, the embryo enters the fetal stage, where it develops into a recognizable form of a mammal and undergoes significant growth and maturation in preparation for birth.

This sequence accurately reflects the progression of mammalian development from fertilization through to the fetal stage.