Why is Polyspermy bad?
Why is Polyspermy bad?
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 happens when two different sperms meet?
What happens when sperm from two different males meet up? In displacement the incoming sperm physically push the sperm of the first mate out of a receptacle in the female where it is stored. Incapacitation is slightly different because it does not even require the sperm of the second mate.
How is Polyspermy blocked?
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.
How does an egg only let one sperm in?
Two mechanisms can operate to ensure that only one sperm fertilizes the egg. In many cases, a rapid depolarization of the egg plasma membrane, which is caused by the fusion of the first sperm, prevents further sperm from fusing and thereby acts as a fast primary block to polyspermy.
How come only one sperm can fertilize an egg?
Once the sperm cells find their way past the zona pellucida, the cortical reaction occurs. This prevents fertilization of an egg by more than one sperm. The cortical reaction and acrosome reaction are both essential to ensure that only one sperm will fertilize an egg.
What prevents more than one sperm from fertilizing an egg?
As the sperm approach the egg, they bind to the zona pellucida in a process known as sperm binding. By creating a new barrier and destroying the initial interface between sperm and egg, the cortical reaction prevents polyspermy, or the fertilization of a single egg by multiple sperm.
What is the slow block to 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 are the 4 steps of fertilization?
The stages of fertilization can be divided into four processes: 1) sperm preparation, 2) sperm-egg recognition and binding, 3) sperm-egg fusion and 4) fusion of sperm and egg pronuclei and activation of the zygote.
