Day 1: The Journey Begins

The Egg Yolk

An infertile and a fertile egg. Can you tell the difference? The white chalazae is much more prominent in the infertile egg. However there is no correlation between fertility and the size of the chalazae. The chalazae is composed of mucin fibers; mucin is a special kind of structural protein. The chalazae holds the yolk in place within the egg.

In the infertile egg, on the left, the nucleus is merely a light spot on the yolk. The egg on the right is fertilized. In the fertilized egg the ovum has fused with a sperm to begin forming an embryo. By the time the fertilized egg is laid, many cells are divided on the surface of the yolk and formed a blastoderm. Can you see the difference between the nucleus of the infertile egg and the blastoderm of the fertilized egg? Both are indicated by the blue arrow.

After one day in the incubator, the small white spot seen in the fertilized egg above has grown to the size of a nickel or a quarter.

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