Events that Occur During Fertilization in Animals and Their Stages

Illustration of animals reproducing (Unsplash)

YOGYAKARTA - The fertilization process in animals is one of the most important in the reproductive system. The events that occur during fertilization in animals are certainly related to the meeting of sperm cells with ovum cells in females. However, the events that occur are not as simple as that. This article will discuss how fertilization in animals.

Events that Occur During Fertilization in Animals

In Fertilization and Embryogenesis by BI Sirait it is explained that fertilization is a process in which the egg and sperm cells meet and join. The joining event in fertilization then produces a diploid zygote that is totipotent. It should be noted that the zygote is considered as the forerunner of a new organism produced from marriage or reproduction.

Animal fertilization can naturally occur outside the body (external fertilization) or inside the body (internal fertilization). External fertilization in animals occurs when the process of fertilization of sperm against the ovum occurs outside the female body. Usually this fertilization occurs in the group of fish and frogs.

Meanwhile, internal fertilization is when the sperm fertilizes the ovum inside the female's body and is deposited in the uterus. Many animals undergo internal fertilization such as mammals.

Stages of Fertilization in Animals

Fertilization in animals begins with the maturation of the sex cells (gametogenesis). To understand more, see the explanation below.

Sexual cell maturation

Male (sperm) and female sex cells (ovum) must be equally ready for fertilization. The reason is that only mature gametes can be involved in the fertilization process.

Sperm and egg release

After the genitals mature, each releases sperm and eggs. In external fertilization (e.g. fish, frogs), sperm and eggs are released into the water. In internal fertilization, the male will insert sperm into the female's body. Sperm will then approach the egg cell.

Sperm and ovum meeting

In this process, sperm have a more active movement to reach the ovum. In external fertilization, sperm will try to swim in the water to reach the egg. The same thing also happens in internal fertilization, only that the sperm will swim through the female reproductive tract until it reaches the ovum.

Sperm penetration

When it is successfully attached to the outer layer of the ovum, the sperm will release acrosomal enzymes. These enzymes are useful for dissolving the protective layer of the egg such as cumulus cells and the zona pellucida so that it can enter. The enzyme is released through the head of the sperm which is called the acrosomal reaction.

Membrane fusion and core unification

When it succeeds in entering the nucleus, the sperm and ovum will join (fusion). This is the fusion that occurs in fertilization to form a diploid zygote with a complete number of chromosomes. At the same time, there is also a polyspermic block, which is a mechanism that prevents other sperm from entering.

Zygote formation

After the fusion, the development of the zygote into an embryo begins. The zygote is considered the first cell of a new individual.

That is the event that occurs during fertilization in animals. Visit VOI.id for other interesting information.