Two Sperm Fertilisng an Egg at once

dudara

Watching a TV program last night bought up a discussion. Can two sperm penetrate the human egg at the same time? And if so, only one will fertilise it, right?

I was trying to recall Leaving Cert biology. Once the sperm enters the egg, it discards it "tail" and the egg forms a barrier that will not let any other sperm in. But can two enter at approx the same time?

cregser

I don't know. But I do know that Leaving Cert syllabuses are simplified somewhat. Surely the egg can't instantaneously form a barrier blocking all other sperm.

wheresthebeef

from what we were told in LC biology. the protective layer that forms does so extremely quickly. almost instantaneously. so yes it can be that quick.

also if for some reason an egg were to contain three haploid nuclei, my understanding is that the normal bodily systems of regulation would see the cell as deformed and the cell would be destroyed by the bodies cell suicide mechanism (cant remember the name for it cyto-something : i cant be bothered to check my notes. Biology exam is over)

Either that or one of the two nuclei would fuse with the ova's nuclei and form a diploid nucleus. and leave the other genetic material redundant.

Lex Luthor

the first sprem to fertilise the egg is the winner....all the rest have no chance, they just hang around outside until the die....

Bamboozled

The first sperm once it enters the outer part of the egg, secretes chemicals and hormones that reject any other sperm trying or getting in.

Gurgle

I thought...
Fraternal twins were from 2 sperms and identical twins were from one sperm where the fertilized egg split...

But I didn't even do leaving cert biology.
(Electrons are way easier to understand)

DrIndy

No and if they did, then the resulting embryo would be triploid and would not survive mitosis. It is not possible to have a viable cell. This is in contrast with plants where triploid and even tetraploid hybrids grow well. The extra energy needed to duplicate the extra DNA confers a disadvantage, but the extra growth development from the extra DNA there offers better seeds etc... Many of the farm variety of grain are triploid or tetraploid.

A reaction or rather instantaneous chain reaction occurs in the ova when a sperm head encounters the wall that INSTANTLY seals it off. In the very rare event of a absolutely instantaneous event of two or more sperm encountering an ova, then it would not be viable and the lady in question would never realise as she would have a normal menstrual cycle.

Another interesting fact is the huge amount of foetuses that are spontaneously aborted in the first trimester because of gross genetic damage only a fraction reach full term. Any woman with this simply thinks they have a late and unusually heavy period (not an abnormal event in itself) and thinks nothing of it. Its a miracle of genetic control and development that we are even half normal!

snappieT

Gurgle wrote:

I thought...
Fraternal twins were from 2 sperms and identical twins were from one sperm where the fertilized egg split...

But I didn't even do leaving cert biology.
(Electrons are way easier to understand)

AFAIK fraternal twins occur when the female produces 2 eggs in a given period cycle, and both are fertilised.

DrIndy

snappieT wrote:

AFAIK fraternal twins occur when the female produces 2 eggs in a given period cycle, and both are fertilised.

Thats right.......

dudara

DrIndy wrote:

A reaction or rather instantaneous chain reaction occurs in the ova when a sperm head encounters the wall that INSTANTLY seals it off. In the very rare event of a absolutely instantaneous event of two or more sperm encountering an ova, then it would not be viable and the lady in question would never realise as she would have a normal menstrual cycle.

Another interesting fact is the huge amount of foetuses that are spontaneously aborted in the first trimester because of gross genetic damage only a fraction reach full term. Any woman with this simply thinks they have a late and unusually heavy period (not an abnormal event in itself) and thinks nothing of it. Its a miracle of genetic control and development that we are even half normal!

That's a perfect answer to my question. Thanks a million. I knew that a large amount of pregnancies were spontaneously aborted early in the first trimester, I just didn't know that the rare chance of two sperm entering an ovum would fall into that category

DrIndy

A triploid cell would probably not even be capable of initial division and it would certainly not be able to form any coherent structure resembling a foetus as the genetic load of one set of genes would derange further.

Occasionally, there are strange developments. The genes in a sperm and only a sperm are needed to form a placenta and the genes in the ovum to form the foetus itself (but ALL are needed to form a human). In rare events where a sperm fertilises an empty egg cell and successfully manages to duplicate its genes or the sperm genes are duplicated twice in an egg cell (a triploid cell) - then a hydatidiform mole is created. Molar pregnancies are when the placenta only grows and keeps growing without a foetus. These can occasionally turn into cancer. Molar pregnancies are more common in those who have had one before, so there is a tendency for those women to form empty ova.

When an empty sperm fertilises an ovum and the female genes only duplicate, a miniature foetus forms, however, without the paternal genes, cannot form a placenta and thus dies off quickly.

This is an interesting adaptation to ensure that genes are mixed and self-cloning cannot occur (which could occur by pure chance of a set of chromosomes duplicating in an egg cell and then multiplying). No ovum can grow without a placenta, which can only be derived from sperm.

dudara

OK, with all that can go wrong, I'm never having kids!!

DrIndy

Anything can go wrong any time, I wouldn't dwell on it! As I said previously it is in fact a miracle we were born even half normal!

Incidence of hydatidiform moles is 1:1000 to 1:1500 pregnancies, the incidence of malignant conversion is low and when it occurs, can be readily treated.
http://www.fpnotebook.com/OB64.htm