Fertilisation

Fertilisation is a process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.

Process

The process of fertilisation involves several stages:

1. Contact: The sperm makes contact with the ovum's protective outer layer, the zona pellucida.
2. Acrosomal reaction: The sperm's acrosome releases digestive enzymes to break down the zona pellucida.
3. Sperm binding: Proteins on the sperm head bind to the zona pellucida.
4. Cortical reaction: The ovum releases enzymes to harden the zona pellucida and prevent other sperm from binding.
5. Fusion: The sperm and ovum plasma membranes fuse, allowing the sperm to enter the ovum.
6. Activation: The ovum completes its second meiotic division, forming the mature ovum and second polar body.
7. Nuclear fusion: The sperm and ovum nuclei fuse to form the diploid zygote.

Consequences

Fertilisation initiates the development of a new individual organism, starting with the formation of the zygote, which develops into an embryo and eventually a fully formed individual. It also determines the genetic makeup of the new individual, including its sex.

See also

• Reproduction
• Sexual reproduction
• Sperm
• Ovum
• Zygote
• Embryo

References

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  Sperm approaching egg

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  Diagram of acrosome reaction

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  Human fertilization

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  Fertilisation