Question

Embryonic Development

a. Explain the anatomical differences between a gamete, zygote, blastomere, morula, and blastocyst.

Answer 1

The first week of human development comprises:

1. Gamete approximation and fusion of gametes
2. Fertilization
3. Mitotic cleavage of blastomeres
4. Morula formation
5. Blastocyst formation
6. Implantation of blastocyst

Here is the anatomical differences among them:

GAMETE	ZYGOTE	BLASTOMERE	MORULA	BLASTOCYST
Haploid (one set of dissimilar chromosomes) sex cell.In male it is known as sperm and in female as oocyte (egg).	Diploid (complete genetic material or carries paired chromosomes) cell. Fertilization between oocyte and sperm results in zygote formation	Zygote fist divides in a two cell state known as blastomere	4 days after fertilization when zygote contains 16 to 32 blastomeres it is known as morula.	5 days after fertilization, morula eventually develops into 50-150 cells stage known as blastocyst
In male is is located in testis and in female located in ovary	It is found in female only in the fallopian tube of reproductive system	Earliest mitotic product of fertilized oocyte. These mitotic division continue and results in grouping of cells called blastomeres	Cells start differentiating anatomically into inner cell mass (ICM)and outer cell mass	Blastocoel is formed by active pumping of fluid by outer cell mass to inner space of blastocyst
Morphologically sperm looks like tadpole. Oocyte is large and spherical	Spherical in shape	Totipotent. That is, it can develop from a single cell to completely fertile adult organism	Cell mass is surrounded by zona pellucida	This expansion of blastocyst leads to thinning of zona pellucida and by rupturing it  embryo hatches
Sperm is motile and oocyte is non-motile	Non-motile	Size of embryo remains same, as cells divide into smaller cells	The group of cells present in the inner cell mass(ICM) and outer cell mass leads cavitation of morula and determine transition to blastocyst	Other group of cells lining inner side of zona pellucida and surrounding ICM are known as trophectoderm cells. Which give rise to fetal placenta.
Gametes by fusing sexually give rise to zygote	Zygote develops into fetus		ICM is pluripotent and eventually form embryo proper	Hallmark of blastocyst formation is fluid filled blastocoel, ICM and trophectoderm cells.Trophectoderm cells fully differentiated into trophoblast.