Eggs

T

TheAlphaWolf

Registered Senior Member
Ok, so what exactly goes on with chicken/bird eggs? they start out as one cell... before it's fertilized... but what is it? Is the oocyte stuck to the yolk? or is it the yolk itself? or the whole egg? I've heard that the biggest cells in the world are ostrich eggs, but I don't quite believe it.
When is it fertilized?
I kind of know what goes on with insect eggs (at least Drosophila melanogaster), but how do reptile eggs and mammal eggs (monotremes) compare to chicken eggs? how about fish and all the other types of eggs out there?
 
Chickens lay eggs regardless of whether they have mated. If a chicken has mated, then her ovum will have been fertilized in the oviduct and the egg will have an embryo growing inside when it is laid. If she hasn’t mated, her eggs will have the unfertilized ovum inside. The eggs that we buy at the supermarket are unfertilized.

Here is a good description…

http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgeneral%2Fans_023.html

Fish are interesting. Some fish are live bearers – they have internal fertilization and internal development. Alternatively, some fish have internal fertilization but external development. Alternatively again, some fish have both external fertilization and development.<P>
 
Interesting. Ok, so Is this right?
the female produces a small egg cell, that normally gets fertilized. The yolk forms near/in/on the cell, but it is NOT a part of the cell right? then the egg white, which is NOT part of the cell either, is put around the egg cell and the yolk... and then the egg shell and stuff... which is also NOT part of the egg cell...
all the while the embryo is starting to divide and stuff and develop just like any other normal animal right? with the blastula and gastrula and all those other stages... feeding on the yolk/egg white...
right?
then why the heck do people say that the biggest cell in the world is an ostrich egg? Ok sure, there may be only one cell in the whole egg, but the whole egg is NOT a single cell!
 
Well, the link says it better than I could......

Oocytes are produced in the ovary, packaged with yolk within a thin protein membrane, and released one at a time into the funnel-like infundibulum of the oviduct. The oviduct is a tubular passageway leading from the ovary to the outside world. It is also an assembly line in which the various layers of the egg are constructed. After an oocyte-yolk package is released into the infundibulum, it lingers there for about 20 minutes. If sperm are present, then the oocyte is fertilized and becomes an embryo. But if no sperm are around (that is, if the hen has not mated), then the egg still proceeds down the assembly line of the oviduct. In this assembly line, albumen (egg white) is added around the yolk, shell membranes are added, and the shell itself is constructed. Finally, the complete egg is pushed through the vagina and out the cloaca.

If the egg has been fertilized, then the embryo inside has already divided several times but remains a group of unspecialized cells. When the egg is incubated at about 37 to 38 °C, the embryonic cells differentiate to form a chick, which will hatch after 21 days. If the egg has not been fertilized, then the oocyte within will never grow or divide, and the egg will never hatch. The eggs you buy at the supermarket are eggs that have never been fertilized.
Click to expand...
You are correct that the yolk and albumen provide nutrition for the growing embryo.

As to whether an ostrich ovum is the largest cell in the world, I do not know. I have never heard this before. Ova are very large cells, probably the biggest cell type in the body of vertebrates. The statement might conceivably be true. If, however, the statement comes from the misunderstanding that the entire contents of an ostrich egg is the ovum, then it is likely to be false.<P>
 
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