Arrange the following events of human embryo development in a correct sequence:

(A) Blastocyst formation

(B) Implantation

(C) Formation of morula

(D) Cleavage in zygote

Choose the correct answer from the options given below:

(D), (C), (A), (B)

The correct answer is Option ( 2)- (D), (C), (A), (B)

The events of human embryo development or the process of implantation can be explained as follows:

1. Fertilization results in the formation of a diploid zygote.

2. As zygote moves through the uterus, mitotic divisions occur in the zygote that results in the formation of blastomeres.

3. Embryo with 16 celled-stage is known as a morula.

4. Morula undergoes further cleavage and develops into a blastocyst. The cells of the blastocyst get arranged into an outer layer called trophoblast and inner cells called inner cell mass.

5. Trophoblast layer of blastocyst gets attached to the endometrium while inner cell mass differentiates to form an embryo.

6. After attachment, the uterine cells divide rapidly and causes the blastocyst to become embedded in the endometrium of the uterus. This is called implantation and this leads to pregnancy.