Fertilized vs. Non-fertile
The rooster must be present for an egg to be fertilized. The eggs that you buy at the supermarket are typically from hens that are raised without a rooster being present. Roosters are not necessary at egg farms where eggs are produced for human consumption and not incubation. Eggs for incubation are grown at special farms called breeder farms where roosters are present with the hens.
The next time you break open an egg; look for the germinal disc. You will see that supermarket eggs are infertile.
Did you know you can determine if an egg is fertile or not by looking at the germ spot? The germ spot is the white spot on the yolk. The non-fertile germ spot contains only the female's cells and looks like a solid white spot. In a fertile egg the germ spot contains both the female and male cells. This allows cells to divide and the spot grows while the rest of the egg is being built in the female's oviduct. Because of this growth the fertile germ spot on the yolk looks like a circle with a somewhat clear center.
Non-Fertile egg, Notice the Germinal spot just above center on the Yolk. It appears as solid white spot.
Fertile Egg. Notice the germinal spot looks larger and like a circle in this fertile egg.