Fertilization is the key to biological reproduction. In humans, sperm cells in males and egg cells in females are the reproductive cells. Each reproductive cell contains 23 thread like structures called chromosomes which carry the traits or characteristics from the parents to offspring.
Egg cell with sperms
The sperm is composed of the head and the tail. the head contains 23 chromosomes. The tail is a whip-like structure that enables the sperm to swim to where the egg cell is. On the other hand, the egg cell is a round structure that contains the nucleus inside and is covered with membrane. The nucleus contains the female chromosomes.
When a single sperm enters the ovum, the process is known as fertilization. This fertilization must occur while the egg cell or ovum is still in the fallopian tube.
The successful sperm initially binds to the outer layer of the ovum through the hook-like structure called a receptor on its surface. Different species of animals have different matching receptors. This is why fertilization is only possible between a male and a female of the same species.
The egg cell is now called a zygote. It immediately begins to multiply by normal cell division and multiple duplication or replication. Cell division and replication continue until a hollow ball, called a morula, is formed. This morula moves from the Fallopian tube into the uterus and implants itself on the uterus lining. Then embryonic development starts.