What is the fast block to polyspermy?
The fast reaction is known as the fast block to polyspermy, which is enabled by an electric charge in the plasma membrane of the egg. When the binding of the first sperm is done, the membrane potential of the egg changes to the positive side by 20 mV.
Do polyspermy blocks work in animals?
Electrical polyspermy blocks operate in many animal species, including frogs, clams, and marine worms, but not in the several mammals that have been studied (hamster, rabbit, mouse). In species without an electrical block, polyspermy is usually prevented by secretion of materials that establish a mechanical barrier to polyspermy.
What causes electrical polyspermy block?
This "electrical polyspermy block" is thought to result because a positively charged molecule in the sperm surface membrane is repelled by the positive charge at the egg surface.
What is the slow block to polyspermy in a sea urchin?
Slow Block to Polyspermy - Cortical Granules The slow block to polyspermy in the sea urchin embryo consists of a physical barrier to further sperm penetration into the egg. Cortical granule exocytosis results in the formation of the fertilization envelope (often called the fertilization "membrane", even though the structure is not a true membrane).
What is the fast and slow block to polyspermy?
1) FAST BLOCK = electrical barrier, preventing fusion of sperm p.m. and egg p.m.; Slow Block is mechanical block to polyspermy, i.e. the fertilization membrane., which hardens and is impervious to further sperm.
What is the slow block to polyspermy due to?
Slow block of polyspermy In mammals, in which fertilization occurs internally, fewer sperm reach the fertilization site in the oviduct. This may be the result of the female genital tract being adapted to minimize the number of sperm reaching the egg.
Do humans have slow block to polyspermy?
Enzymes such as hydrolase, proteinase, and peroxidase, which are contained in the cortical granules, prevent the penetration of following sperm by modifying the structure of the sperm receptors such as ZP2 and ZP3 (“slow block” to polyspermy) and by hardening the ZP [5,11].
What are two blocks to polyspermy?
0:343:47Fast Block To Polyspermy in Sea Urchin - YouTubeYouTubeStart of suggested clipEnd of suggested clipThat blocks to polyspermy is achieved via two pathways slow blocks to polyspermy. And fast blocks toMoreThat blocks to polyspermy is achieved via two pathways slow blocks to polyspermy. And fast blocks to polyspermy. The first block to polyspermy is electrical block to the sperms.
Which of the following causes the block to polyspermy during Fertilisation?
In humans, block to polyspermy is attributed to “oocyte membrane block,” also known as “fast block,” which primarily involves depolarization of the oocyte membrane after binding of the first spermatozoa and transiently prevents any subsequent sperm binding to the oocyte.
Which of the following is considered as fast block to check polyspermy?
During fertilisation, the fusion of sperm depolarises the membrane of egg cell and causes fast block to polyspermy.
How does zona pellucida prevent polyspermy?
Once a sperm comes In contact with the zona pellucida of the ovum, it induces changes In its membrane. These changes prevent the entry of other sperm into the ovum and thus prevent polyspermy.
What reaction is Zona?
Zona reaction refers to a modification of the zona pellucida in response to fertilization, which alters the solubility and binding properties of the zona pellucida, and leads to a slow block to polyspermy. Mammalian Fertilization.
What causes polyspermy in humans?
Recently, it was found that an abnormal zona pellucida is one of main causes of polyspermy in human eggs. A high proportion of polyspermy has resulted from the use of a high concentration of capacitated spermatozoa at the site of fertilization, irrespective of in the in vivo or in vitro environment.
What causes the slow block to polyspermy quizlet?
Fast block to polyspermy occurs early in the acrosomal reaction and involves depolarization of the egg cell membrane during the sperm/egg cell membrane fusion. Slow block to polyspermy occurs later in the cortical reaction and involves receptor clipping.
How fast do blocks stop polyspermy?
Prevention of Polyspermy The fast block to polyspermy, which has been best studied in sea urchins, consists of a rapid electrical depolarization of the plasma membrane of the egg. The resting membrane potential of the egg changes from about − 70 to + 10 mV within 2–3 s after fusion of the spermatozoon with the egg.
Physiological polyspermy
Physiological polyspermy happens when the egg normally accepts more than one sperm but only one of the multiple sperm will fuse its nucleus with the nucleus of the egg. Physiological polyspermy is present in some species of vertebrates and invertebrates.
Blocking polyspermy
Polyspermy is very rare in human reproduction. The decline in the numbers of sperm that swim to the oviduct is one of two ways that prevents polyspermy in humans. The other mechanism is the blocking of sperm in the fertilized egg.
Evolutionary advantage
Female defenses select for ever more aggressive male sperm, however, leading to an evolutionary arms race. On the one hand, polyspermy creates inviable zygotes and lowers female fitness, but on the other, defenses may prevent fertilization altogether.
Gametogenesis, Fertilization and Early Development
Abstract Polyspermy is a lethal condition where more than one sperm nucleus interacts with the female nucleus. This article looks at how animals avoid this condition in nature and shows that sperm numbers are regulated in various ways to ensure low sperm–oocyte ratios at the site of fertilization.
Assisted Reproduction
Abnormal fertilization by conventional in vitro fertilization is mainly associated with abnormal polyspermy, due to the dispermic oocyte penetration resulting in tripronuclear (3PN) oocytes.
Glycoproteins II
One of the important roles of mammalian cortical granules may be to block polyspermy in the perivitelline space [45]. In fish, fertilizing sperm enters through a special opening in the egg envelope called micropyle. The diameter of the micropyle in most fish is usually just large enough to allow a single sperm.
Gametogenesis, Fertilization and Early Development
Keizo Tokuhiro, Jurrien Dean, in Encyclopedia of Reproduction (Second Edition), 2018
Plant Development and Evolution
Liang-zi Zhou, Thomas Dresselhaus, in Current Topics in Developmental Biology, 2019
Comparative Reproduction
Ryusaku Deguchi, Noritaka Hirohashi, in Encyclopedia of Reproduction (Second Edition), 2018
Fertilization
When a spermatozoon has fused with an egg, the entry of other spermatozoa into the egg ( polyspermy) must be prevented, or abnormal development is likely to result. Two blocks to polyspermy, fast and slow, are typically present in vertebrate fertilization.
Overview
Blocking polyspermy
Polyspermy is very rare in human reproduction. The decline in the numbers of sperm that swim to the oviduct is one of two ways that prevents polyspermy in humans. The other mechanism is the blocking of sperm in the fertilized egg. According to Developmental Biology Interactive, if an egg becomes fertilized by multiple sperm, the embryo will then gain various paternal centrioles. When this happens, there is a struggle for extra chromosomes. This competition causes disarrayment in cleavage …
Physiological polyspermy
Physiological polyspermy happens when the egg normally accepts more than one sperm but only one of the multiple sperm will fuse its nucleus with the nucleus of the egg. Physiological polyspermy is present in some species of vertebrates and invertebrates. Some species utilize physiological polyspermy as the proper mechanism for developing their offspring. Some of these animals i…
Evolutionary advantage
Female defenses select for ever more aggressive male sperm, however, leading to an evolutionary arms race. On the one hand, polyspermy creates inviable zygotes and lowers female fitness, but on the other, defenses may prevent fertilization altogether. This leads to a delicate compromise between the two, and has been suggested as one possible cause for the relatively high infertility rates seen in mammalian species. In some species, polyspermy is allowed to happen to result i…
See also
• Cortical reaction
Further reading
• Ginzberg, A. S. 1972. Fertilization in Fishes and the Problem of Polyspermy, Israel Program for Scientific Translations, Jerusalem.
• Jaffe, L. A. & M. Gould. 1985. Polyspermy-preventing mechanisms. In C. B. Metz & A. Monroy (editors) Biology of Fertilization. Academic, New York.Brendon magero; 223–250.
External links
• Animation of polyspermy