You would only know by candling the egg. Brown eggs are a slight bit harder to candle than white ones. Candling means to shine a very strong light into the egg and observe shadows within. If there are no shadows or dark areas withing the egg then it either has not started embryo development or is not fertile.
As a consumer you may think that it is difficult for you to know if the eggs you buy are fertilized. There are no exterior or outward signs on the egg, and finding the germinal disc (also referred to as the "bullseye") on the egg yolk is not something many people can do, as it is so small. However, nearly all eggs sold in grocery stores are infertile, because the hens that lay those eggs generally live their entire lives in small enclosures on factory farms and never see a rooster. Free-range eggs, those from hens not kept in such enclosures, will be labeled, and most farms that produce free-range eggs still restrict hens from being near roosters, but some will label their eggs as being produced with roosters in the flock. Only those eggs produced with roosters in the flocks can possibly be fertilized.
If you buy eggs from a local farm, and they have a rooster among the flock, you can be pretty sure the eggs you get are fertile. Fertilized eggs are really no different nutritionally, than the non-fertile eggs purchased at a supermarket. The only differences in taste or nutrition between supermarket eggs and farm eggs are due to the wider variety in the hens' available diets on farms, which allow them to produce richer-tasting, more nutritional eggs.
Although an egg shell may seem to be opaque, it is actually translucent. If you put a bright light next to an egg (historically, candles have been used) you can see what is inside the egg. If the egg has been fertilized, you can see the embryo. It has a reddish color because it has blood, which an unfertilized egg does not have.
you know if the egg is fertilized if you missed your period.
Fertilized eggs are not brown because they have been fertilized. The chickens do not colour code the one's that are viable and leave the rest of them white. Any egg of whatever colour can be fertile. I have incubated white, brown, green and blue eggs many times. Most have hatched. The egg colour comes from the various breeds of chicken that laid the egg, it does not change colour for any reason unless you dye them at Easter.
It is necessary for an egg to be fertilized so the egg can hatch.
A fertilized egg cell is when a sperm enters an egg. The result is a fertilized egg cell, or a zygote.
Yes, a zygote is a fertilized egg.
The gametes, or "sex cells" - the sperm and ovum (egg) - become the fertilized egg (zygote) when they fuse.
A fertilized egg implants into the Uterus.
The sperm doesn't have to. Once the egg is fertilized it stays fertilized.
When a bird's egg is fertilized, a chick is developing inside.
A fertilized egg cell is when a sperm enters an egg. The result is a fertilized egg cell, or a zygote.
No
The fertilized egg becomes an embryo and later becomes a fetus.
A fertilized egg is an egg that is fertilized - in short terms, it can be incubated and a chick will hatch from it after incubation.