MadSci Network: General Biology

Re: How come sometimes there are two yolks in one egg?

Area: General Biology
Posted By: Marcy LaViollette, Senior, chemical engineering, Capital High School
Date: Mon Nov 17 19:40:38 1997
Area of science: General Biology
ID: 876685281.Gb

Twins can be created two different ways. One way is for a single fertilized egg to split into two. The resulting children are called identical twins, because they will have the same DNA, and look alike. Another way is for two eggs to be produced by the mother, instead of the one egg per cycle that is normally released. This is called fraternal twins, the children will have different DNA, and will look no more alike than any normal brother or sister. Inside a human mother is a lining that encases the baby. Inside a chicken this lining is the egg shell.

In a chicken, fraternal twins are known to us as two complete eggs with seperate shells. Identical twins, on the other hand, come out as one egg shell with two yolks inside. Both of these yolks are eggs as I explained above. Eggs as you buy them in a store are screened and all imperfect eggs are removed. This is why you rarely find any double eggs.

Since I have never raised chickens, I don't personally know if it is possible for these twin chickens to actually hatch. I see no reason why they wouldn't be able to survive. It is possible on the other hand that one chick would be the stronger and break open the shell before the other was ready for the world.

To answer the question of their survival rate, I suggest you ask Bart Pals, the Vice President of the American Poultry Association. Or you could try Donald Firsching who has a chicken web page.

Good luck!

Keep asking questions!
-Marcy LaViollette

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