Question

At fertilization, what happens to the sex cells?

They keep half of their chromosomes.

Half of the cells copy their DNA twice.

Their chromosomes join to form one nucleus.

One becomes an egg, and one becomes a sperm cell.

Answer 1

Their chromosomes join to form one nucleus.

Step-by-step explanation:

At fertilization, when sperm of male enters into the ova or egg of female, their chromosomes join to form one nucleus.

During the process of fertilization, several reaction occurred to form a zygote. Once the sperm reaches the egg, it releases some enzymes to degrade the zona pellucida (layer around the egg) and enters the egg for fusion to give one zygote or nucleus.

Hence, the correct answer is "Their chromosomes join to form one nucleus."