Many people wonder – what part of a chicken egg actually becomes the chicken? This seems like a simple question, but the process of a chicken developing from an egg is complex and fascinating. In this article we’ll take a close look at chicken egg anatomy to understand exactly how a chick forms inside the humble egg.
The Main Components of a Chicken Egg
First, let’s go over the key parts of a chicken egg:
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Shell – The hard, porous outer covering that allows gas exchange while protecting the embryo Made mostly of calcium carbonate
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Shell Membranes – Two thin membranes lining the shell that provide additional protection.
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Air Cell – Forms at the large end of the egg and provides the chick’s first breath at hatching.
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Albumen (Egg White) – Primarily water but also contains proteins. It cushions the yolk and provides hydration.
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Yolk – Contains all the egg’s fat and most of the vitamins and minerals. It’s the food for the developing chick.
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Chalazae – Ropey strands that anchor the yolk in the center of the egg.
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Germinal Disc – A small white spot on the yolk’s surface. This is key!
The Germinal Disc Holds the Genetic Blueprint
So what part becomes the actual chicken? It’s the germinal disc (also called the blastoderm) on the surface of the yolk. This disc is barely visible, but it contains the genetic information that will grow into a chick.
When the egg is fertilized by a rooster, the nucleus of the ovum is located in the germinal disc. The disc starts dividing into more and more cells after fertilization, forming the early embryo that will become the chick. So while the yolk provides food, the physical chick grows from that tiny germinal disc.
Inside the Germinal Disc: DNA to Develop the Chick
The germinal disc is where the magic happens. After fertilization by a rooster, rapid cell division takes place in the disc, forming a cluster of cells called the blastoderm.
The blastoderm consists of:
- Ectoderm – forms skin, feathers, nerves
- Mesoderm – forms muscle, bone, blood
- Endoderm – digestive tract and organs
This three-layered structure lays out the foundation for every cell and tissue in the chick’s body. The genetic information needed to form the beak, wings, and every other part is present in the microscopic cells of the germinal disc.
The Yolk Nourishes the Growing Embryo
As the germinal disc divides and the embryo develops, the yolk provides sustenance. This nutrient-dense yellow blob contains proteins, fats, vitamins and minerals that the chick relies on for growth during incubation.
The yolk is absorbed into the chick’s body in the days before hatching. What remains at hatching is the yolk sac, which the baby chick will continue to draw nutrients from in its first few days of life.
- The germinal disc contains the genes and blueprint to grow the chick.
- The yolk has the food and energy to power this growth.
Other Key Parts Supporting Development
While the germinal disc and yolk are most critical, the other components of the egg also play roles:
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The albumen or egg white contains additional proteins and acts as a cushion against damage.
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The membranes and shell protect the embryo and allow gas exchange.
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The chalazae keep the yolk stable so the embryo can access nutrition.
Every piece of the puzzle is needed for the chick to fully form and hatch!
From Egg to Chick: A 21 Day Journey
Once an egg is fertilized and incubation begins, it takes approximately 21 days for the miracle of development to be complete and a chick to hatch.
Those 21 days can be summarized as follows:
Day 1: Fertilization – the germinal disc begins dividing
Day 3: Early embryos develops with primitive structures
Day 8: Feather tracts and beak visible
Day 10: Legs, toes, wings visible – embryo looks like a chick!
Day 21: Fully developed chick hatches from egg
The orderly progression from single cell to recognizable chick is one of nature’s wonders. With the right conditions, the genetic pattern in the germinal disc unfolds seamlessly into a living, breathing ball of fluff!
Key Takeaways on Egg Anatomy
- The germinal disc contains the genes to build the chick
- The yolk provides food for growth
- The albumen, membranes, and shell support the process
- In 21 days, a chick forms and hatches!
Understanding the anatomy of the chicken egg gives insight into the incredible journey from fertilization to hatching. Next time you crack open an egg, remember that with the right start, the microscopic cells of the germinal disc can create a life!
Outer and Inner Membranes
Between the shell and the albumen, or egg white, there are two other membranes: the outer shell membrane and inner shell membrane. These shell membranes function to protect the contents of the egg from bacterial invasion and prevent moisture from leaving the egg too quickly.
Shortly after being laid, the two membranes separate at one end of the egg, forming a small pocket of air called the air cell. This happens when the egg begins to cool from body temperature to ambient temperature. The contents of the egg contract, and the two membranes separate. This separation of membranes can be used to indicate freshness. The longer an egg sits, the more moisture it will lose and the more it will contract, making the air cell grow larger as the egg ages.
Next, we get to the albumen—or what most people refer to as the egg white. There are two portions of the albumen: the outer thin albumen, which is a fluid layer, and the inner thick albumen, which is the portion closest to the yolk.
Both portions of the albumen are the fluid media for chick development and help absorb any movement the embryo may make during development. This part of the egg is extremely high in protein!
The star of the show is the yolk, of course, which is bright yellow and neatly held in the center of the egg. The egg yolk serves as nutrients for the growing chick, which is why it is extremely nutrient dense in both proteins and fats.
The yolk is surrounded by a clear casing that is referred to as the vitelline membrane. This membrane helps keep the yolks perfectly round shape as well as helps prevent egg yolk mottling, which is uneven or patchy coloration of the yolk surface.
If you look closely at a fresh egg, you may notice what looks like small white strings on either end of the yolk. These are called chalazae. They are made of twisted strains of mucin proteins, and their role is to hold the yolk in place during egg formation.
On the surface of the yolk, you can find a small white dot. This is referred to as the germinal disk, or blastodisc, and is the single female cell needed to initiate embryonic development.
If your eggs are not fertile, the blastodisc will remain intact and appear as a solid white dot. However, if your eggs are fertile, the center of the dot will appear yellow. This indicates that the germinal disc has been fertilized—making it now a blastoderm—and has the potential to develop into a chick.
It is important to remember that eggs will only develop embryos if kept at a specific temperature. Without incubation, the blastoderm will never develop further. So don’t worry about eating a fertilized egg! As long as it hasnt intentionally been incubated, you will not be eating an actual baby chicken.
Eggs are a delicious and nutritious part of our diets, but they’re also efficient vessels specifically formed for growing safe and healthy baby chicks. They’re good for us because they’re designed to be good for sustaining a life! Raising your own chickens is amazing for many reasons, and we hope that learning about the composition of an egg will help you appreciate it even more.
In addition to being chicken enthusiasts here at Southland Organics, we make all-natural health supplements for backyard flocks. Our products help your birds stay in peak condition and produce eggs with nice, firm shells. If you have any questions about our products or the parts of a chicken egg, reach out to [email protected] or give us a call at 800-608-3755.
This was written by Alyssa Rauton. With a bachelor’s degree in avian biology and two years of vet school from the University of Georgia under her belt, Alyssa has a wealth of knowledge on chicken health, nutrition and biology as well as a keen understanding of the animal agriculture industry. Alyssa has been writing content and executing research and development for Southland Organics since 2020.
PARTS OF AN EGG | Parts of an Egg and their Functions | Science Lesson
FAQ
Which part of an egg is the chicken?
The yolk has a small white spot on it called the egg cell or germinal disc. This is the part of the egg from which the baby chick develops. The yolk provides food for the baby chick while it is growing in the shell. The albumen is the thick clear substance surrounding the yolk.
Is the white part of the egg the umbilical cord?
No, it’s not a vein or a baby chick’s umbilical cord. It’s actually part of the egg that, although it looks unnatural, is completely normal and necessary for an egg to develop safely. It’s called a chalaza. There are two chalazae in an egg, one that suspends from the top of the shell and one from the bottom.
Is the white part of an egg chicken sperm?
No, the white part of an egg (albumen) is not chicken sperm. It is a protein-rich substance that surrounds the yolk, providing nutrients and protection for the developing embryo. The chalazae, the stringy white strands, are part of the albumen and help keep the yolk centered.
Is the yolk like a placenta?
No, the yolk is not the same as a placenta.