Question

Some important events that take place during fertilisation are given below. Arrange the events in a proper sequence and select the correct option.

(i) Conical reaction
(ii) Sperm entry
(iii) Karyogamy
(iv) Acrosomal reaction

• A. (iv) $\to$ (i) $\to$ (ii) $\to$ (iii)
• B. (i) $\to$ (ii) $\to$ (iii) $\to$ (iv)
• C. (iv) $\to$ (ii) $\to$ (i) $\to$ (iii)
• D. (ii) $\to$ (i) $\to$ (iii) $\to$ (iv)

Answer 1

The correct option is A (iv) $\to$ (i) $\to$ (ii) $\to$ (iii)

• Acrosomal reaction first occurs as a result of the enzymes secreted by the head portion of the sperm and induces it to fuse with the plasma membrane and then penetrate the female egg to fertilize it.
• Cone of attraction is the region where the spermatozoon is about to pierce, the yolk is drawn out into a conical elevation, termed the cone of attraction or reception cone. The cortical reaction includes the fusion of the cortical granules inside the secondary oocyte to fuse with the plasma membrane of the cell, causing enzymes inside these granules to be expelled by exocytosis to the zona pellucida.
• The sperm nucleus then fuses with the ovum, enabling the fusion of their genetic material and as the nuclei of the two fuse together it is referred to as karyogamy.

So, the correct option is (iv) $\to$ (i) $\to$ (ii) $\to$ (iii)