Polyspermy

Polyspermy is a condition in which an egg is fertilized by more than one sperm. This condition is common in many animals, but in humans and other mammals, it can lead to triploidy and other chromosomal abnormalities, which can be lethal.

Overview

Polyspermy occurs when more than one sperm fertilizes an egg. In many animals, this is a normal part of reproduction. However, in mammals, polyspermy can lead to chromosomal abnormalities, such as triploidy, where an organism has three sets of chromosomes instead of the usual two. This can result in severe developmental problems and is often lethal.

Mechanisms

There are two types of polyspermy: external and internal. External polyspermy occurs when multiple sperm fertilize an egg outside of the body, as in many fish and amphibians. Internal polyspermy, on the other hand, occurs when multiple sperm fertilize an egg inside the body, as in mammals.

In mammals, the egg has several mechanisms to prevent polyspermy. The first is the zona pellucida, a thick layer around the egg that blocks additional sperm once the first one has entered. The second is the cortical reaction, in which the egg releases enzymes that harden the zona pellucida.

Despite these mechanisms, polyspermy can still occur. This is often due to problems with the egg or sperm, such as a thin zona pellucida or a high number of sperm.

Consequences

Polyspermy can have serious consequences in mammals. The most common is triploidy, in which the organism has three sets of chromosomes. This can cause severe developmental problems and is often lethal. Other possible consequences include aneuploidy, where the organism has an abnormal number of chromosomes, and hydatidiform mole, a type of pregnancy tumor.

See also

• Monospermy
• Fertilization
• Zygote

References

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