What is the result of polyspermy?
At fertilization, eggs are exposed to multiple sperm but entry of more than one sperm causes polyploidy, polyspermy, which results in abnormal embryo development. To ensure fusion of a single sperm, the egg becomes rapidly intolerant to additional sperm.
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 is polyspermy prevented quizlet?
Polyspermy is the double fertilization of an ovum by two sperm. It is prevented by 3 methods during fertilization: 1) The intracellular wave of Ca2+ that travels across the oocyte membrane and causes hyper polarization after fusion of the sperm and oocyte membranes. This forms a barrier to outside sperm.
What causes the slow block to polyspermy?
Thus, after the first sperm contacts the egg and causes the change, subsequent sperms are prevented from fusing. 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.
Why is polyspermy a problem?
Polyspermy is bad because, in addition to the extra set of chromosomes, a sea urchin sperm donates a centriole. The presence of additional centrioles during the first cell division will result in additional cleavage furrows and incorrect partitioning of the chromosomes (Fig. 7.21).
What is Amphimixis quizlet?
Amphimixis Occurs and Cleavage Begins. Male pronucleus migrates toward the center of ovum, where spindle fibers are forming. The two pronuclei then fuse in a process called amphimixis.
What event is responsible for polyspermy blockage quizlet?
The acrosomal reaction precedes fertilization and involves the sperm penetrating the jellylike coat of an egg. Sodium ions diffusing into the egg cause depolarization of the membrane. Depolarization of the membrane comprises the fast block to polyspermy.
What is polyspermy and how is it prevented?
When a sperm comes in contact with the zona pellucida layer of the ovum it induces changes in the membrane of the ovum to block the entry of additional sperms. This thus prevents the polyspermy and ensures that only one sperm can fertilise an ovum.
What is the slow block of polyspermy?
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 polyspermy How do you avoid that what are the consequences of polyspermy?
An egg must be fertilized by a single sperm only. To prevent polyspermy, the zona pellucida, a structure that surrounds mammalian eggs, becomes impermeable upon fertilization, preventing the entry of further sperm. The structural changes in the zona upon fertilization are driven by the exocytosis of cortical granules.
How is polyspermy avoided?
When a sperm comes in contact with the zona pellucida layer of the ovum, it induces changes in the membrane of the ovum to block the entry of additional sperms. This, thus, prevents the polyspermy and ensures that only one sperm can fertilise an ovum.
What hormones stimulate and increase the excitability of the myometrium quizlet?
Prostaglandin Production: stimulated by estrogens and oxytocin. Increased Excitability of Myometrium: Oxytocin and prostaglandins stimulate the myometrium.