<u>ANSWER:</u>
The correct order is- Zygote, Blastula, Gastrula, Fetus.
<u>EXPLANATION:</u>
- The embryo develops from the zygote which is formed when the gametes fuse in the process of "fertilization".
- The zygote undergoes cell division to form blastula which is a "ball of cells".
- Gastrula leads to the rearrangement of cells of the blastula into three layers that differentiate into different systems of organ.
- The last stage is the fetus which then develops into a baby.
I believe the term for an observable trait of an organism would be called or noted as the organism's phenotype.
