Fertilization by Single Spermatozoid?

[Proteus]

In micrographs, you always see a large number of spermatozoids penetrate the oval wall, not one. What happens to all that DNA, and what determines which genome is used?

 

http://www.falki-design.ch/wordpress/wp-content/uploads/2009/02/befruchtung.jpg

[Cap'n Refsmmat]

Once a single spermatozoid enters, the egg cell wall changes to not allow any others through. So what you see is a large number trying to penetrate the cell wall.

[Mr Skeptic]

As I understand, there is also a much quicker change in the electric charge of the egg.

[jake.com]

Almost always, if more than one sperm enters an egg, the zygote is terminated. I believe it is called a molar birth when it isnt miscarried... I'm not sure though.

[Proteus]

You're right, it's apparently called a partial mole, a kind of hydatidiform mole.

 

The change in electric charge is very interesting. If it's an electrichemical mechanism it would surely explain how it can happen fast enough.

[greenprogrammin]

It is caused by n flux of Calcium if I remember right. I can't remember if it is an influx or out.

[jake.com]

Its in chap 46 of my AP Bio book. It has two parts, the fast block and the slow block. The fast block is at the end of the acrosomal reaction, when the sperm fuses with the egg's cytoplasm. this causes the ion channels to open up and release sodium ions to flow into the egg and change the membrane potential. This change is called depolarization, and it occurs within 1-3 seconds after the sperm fuses with the egg.

 

The second part is called the cortical reaction. since the depolarization only lasts a few minutes, it only blocks sperm for a short time. Numerous vesicles lie just beneath the egg's plasma membrane, in the rim of the cytoplasm called the cortex. within seconds of the fusion, these vesicles, called cortical granules, fuse with the egg plasma membrane, initiation the cortical reaction. cortical granules contain a treasure trove of molecules, which are now secreted into the perivitelline space, which lies in between the plasma membrane and the vitelline layer. the secreted enezymes and other macromolecules together push the vitelline layer away from the egg and harden the layer, forming a protective fertilization envelope that resists the entry of additional sperm. another enezyme is released which clip the remaining sperm receptor proteins.

 

whew. now you know, lol.

[Proteus]

That's amazingly helpful, and the best, most informative post I've ever read on this forum. Thanks for elaborating, it's all noted down.

[mauy]

its hard to understand how people can know this its not like you can ask them

but i still belive you

[jake.com]

That's amazingly helpful, and the best, most informative post I've ever read on this forum. Thanks for elaborating, it's all noted down.

 

btw, humans apparently do not have a fast block mechanism.

[qasim]

In micrographs, you always see a large number of spermatozoids penetrate the oval wall, not one. What happens to all that DNA, and what determines which genome is used?

 

http://www.falki-design.ch/wordpress/wp-content/uploads/2009/02/befruchtung.jpg

hmmmmmmmmmmmmm I think that is a good question. I will think about that