Polyspermy: Difference between revisions

Latest revision as of 11:51, 15 February 2025

Polyspermy[edit]

Polyspermy is a phenomenon that occurs during the fertilization process when an egg is fertilized by more than one sperm. This can lead to abnormal development and is generally prevented by various mechanisms in sexually reproducing organisms.

Mechanisms of Polyspermy Prevention[edit]

In most species, polyspermy is prevented by a series of mechanisms that ensure only one sperm fertilizes the egg. These mechanisms can be broadly categorized into two types: fast block and slow block.

Fast Block to Polyspermy[edit]

The fast block to polyspermy occurs immediately after the first sperm fuses with the egg. This involves a rapid depolarization of the egg's plasma membrane, which prevents additional sperm from fusing with the egg.

Slow Block to Polyspermy[edit]

The slow block to polyspermy involves the cortical reaction, where cortical granules release their contents into the space between the plasma membrane and the zona pellucida. This leads to changes in the zona pellucida that prevent further sperm from penetrating the egg.

Types of Polyspermy[edit]

Polyspermy can be classified into two main types: pathological polyspermy and physiological polyspermy.

Pathological Polyspermy[edit]

Pathological polyspermy occurs when multiple sperm fertilize an egg, leading to an abnormal zygote with too many chromosomes. This often results in developmental failure and is typically lethal.

Physiological Polyspermy[edit]

Physiological polyspermy is a controlled process observed in some species, such as birds and reptiles, where multiple sperm enter the egg, but only one sperm's genetic material fuses with the egg's nucleus. The additional sperm contribute to the activation of the egg but do not contribute genetically.

Consequences of Polyspermy[edit]

The primary consequence of polyspermy is the formation of a polyploid zygote, which usually cannot develop properly. In most cases, the resulting embryo is non-viable due to the imbalance in genetic material.

Related Pages[edit]

@@ Line 1: / Line 1: @@
-'''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.
+== Polyspermy ==
-== Overview ==
+[[File:Physiological_Polyspermy.png|thumb|right|Diagram illustrating physiological polyspermy.]]
-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 ==
+'''Polyspermy''' is a phenomenon that occurs during the fertilization process when an egg is fertilized by more than one sperm. This can lead to abnormal development and is generally prevented by various mechanisms in sexually reproducing organisms.
-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.
+== Mechanisms of Polyspermy Prevention ==
-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.
+In most species, polyspermy is prevented by a series of mechanisms that ensure only one sperm fertilizes the egg. These mechanisms can be broadly categorized into two types: [[fast block to polyspermy|fast block]] and [[slow block to polyspermy|slow block]].
-== Consequences ==
+=== Fast Block to Polyspermy ===
-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.
+The fast block to polyspermy occurs immediately after the first sperm fuses with the egg. This involves a rapid depolarization of the egg's plasma membrane, which prevents additional sperm from fusing with the egg.
+=== Slow Block to Polyspermy ===
+The slow block to polyspermy involves the [[cortical reaction]], where cortical granules release their contents into the space between the plasma membrane and the [[zona pellucida]]. This leads to changes in the zona pellucida that prevent further sperm from penetrating the egg.
+== Types of Polyspermy ==
+Polyspermy can be classified into two main types: pathological polyspermy and physiological polyspermy.
+=== Pathological Polyspermy ===
+Pathological polyspermy occurs when multiple sperm fertilize an egg, leading to an abnormal [[zygote]] with too many [[chromosomes]]. This often results in developmental failure and is typically lethal.
+=== Physiological Polyspermy ===
+Physiological polyspermy is a controlled process observed in some species, such as birds and reptiles, where multiple sperm enter the egg, but only one sperm's genetic material fuses with the egg's nucleus. The additional sperm contribute to the activation of the egg but do not contribute genetically.
+== Consequences of Polyspermy ==
+The primary consequence of polyspermy is the formation of a [[polyploid]] zygote, which usually cannot develop properly. In most cases, the resulting embryo is non-viable due to the imbalance in genetic material.
+== Related Pages ==
-== See also ==
-* [[Monospermy]]
 * [[Fertilization]]
+* [[Cortical reaction]]
+* [[Zona pellucida]]
 * [[Zygote]]
-== References ==
+[[Category:Reproductive biology]]
-<references />
-[[Category:Reproduction]]
-[[Category:Genetics]]
-[[Category:Embryology]]
-{{stub}}
-{{dictionary-stub1}}