polyspermous

Polyspermy refers to the fertilization of an egg by more than one sperm cell, a condition that typically results in developmental abnormalities or failure in most species. In normal fertilization, a single sperm penetrates the egg’s outer layers, triggering a series of biochemical changes that prevent additional sperm from entering—a process known as the fertilization envelope or cortical reaction. Polyspermy disrupts this mechanism, leading to an abnormal number of pronuclei (the nuclei of sperm and egg) within the fertilized egg.

The occurrence of polyspermy varies across species. In humans and many mammals, polyspermy is almost always lethal, as the extra genetic material disrupts cell division and embryonic development. However, in some marine invertebrates, such as sea urchins and fish, polyspermy can occasionally occur without immediately fatal consequences, though it often still results in developmental defects or death. Certain plants and some lower organisms may exhibit polyspermy as a natural part of their reproductive strategy, though this is rare.

The physiological mechanisms preventing polyspermy include the fast block (electrical changes in the egg membrane) and the slow block (physical barriers like the fertilization envelope). When these fail, polyspermy can occur due to genetic mutations, environmental factors, or experimental manipulation. In assisted reproductive technologies, polyspermy is a concern, as it can lead to failed pregnancies or genetic disorders in offspring.

While rare in humans, polyspermy has been documented in cases of in vitro fertilization (IVF) and can sometimes be detected through genetic testing of embryos. Research into polyspermy helps scientists understand fertilization processes and improve reproductive technologies.