Egg shape

The following picture details the inner structure of a chicken egg:

 

taken from: http://food.oregonstate.edu/learn/egg.html

Keeping in mind the picture above, let's explore the structure of the egg.

The egg begins with the germ cell atop the yolk. The germ cell contains the hen's chromosomes. Over time, the germ cell accumulates a white, primordial form of yolk, the white yolk. Close to the time when the hen is preparing to lay the egg, the germ cell accumulates yellow yolk, which is mostly composed of fats and proteins. The color of the yolk reflects the pigments in the hen's diet. The yolk becomes large enough to potentially feed a developing chick for 21 days.

The yolk is released from the hen's ovary into the oviduct, where the germ cell can be fertilized if the hen mates. Most eggs are not fertilized. The egg white forms from proteins secreted here, mainly albumen (albumin proteins particular to eggs). Four alternating thick and thin layers of protein form the egg whites that surround the yolk. The chalazae is a twisted albumen anchor that connects the yolk to the shell. It allows the yolk to rotate while suspended in the middle of the egg.

On the outer side of the white, lies an antimicrobial protein membrane that connects everywhere except for the air pocket that is available for the hatching chick to breathe. The shell consists of calcium carbonate and proteins. Finally, a thin proteinaceous cuticle covers the shell which initially plugs the pores in the shell. The cuticle prevents water loss and blocks bacteria from entering the egg. Gradually, the cuticle fractures for the purpose of allowing oxygen in for the developing chick.

The color of the egg comes along with the cuticle. Egg color is determined by the genetic make up of the hen. If the hen has white plumage, the egg is white. If the hen is pigmented, such as the Rhode Island Reds, the eggs are brown. There is neither a nutritional nor a taste difference between brown eggs and white eggs.

Note: This post reminded me of one of my favorite essays by E.B. White, Riposte, where he discusses the preferences of the brown egg versus the white egg. I highly recommend it for an entertaining, and logical view of color.