When fertilization occurs that leads to formation of a zygote, which of the following processes takes place?

Step 1: Analyze the question The question asks what happens during fertilization when a zygote forms.

Step 2: The concept Fertilization is the fusion of the male gamete (sperm) with the female gamete (ovum or egg cell). Its key result is the union of the two haploid nuclei. This restores the diploid number of chromosomes (2n) in the zygote.

When a sperm reaches the egg:

• The head, which contains the nucleus with the father's genetic material, enters the egg.
• The tail (flagellum) is used only for swimming. It usually stays outside or degenerates and does not contribute to the zygote.
• The sperm nucleus (n) fuses with the egg nucleus (n) to form the zygote (2n).

Step 3: Evaluate the options

• A. The tail of the sperm fuses with the egg cell. Wrong. The tail does not enter or fuse with the egg.
• B. Both tail and head fuse with the egg cell. Wrong. The tail is left behind.
• C. The nucleus of the sperm fuses with the egg cell. Correct. The sperm nucleus enters the egg and fuses with the egg nucleus, forming the diploid zygote.
• D. The egg cell develops on its own without the sperm. Wrong. This describes parthenogenesis, not fertilization.

Answer: C

Exam tip: Remember "the tail is for travel, the head is for heredity." Only the head's nucleus carries genes into the egg. Fertilization means fusion of nuclei: n + n = 2n.