Introduction:

Chick embryos are a widely used model organism for studying development due to their accessibility and similarity to human development. Chick embryo development undergo a series of morphological changes over a period of 21 days, beginning with fertilization and culminating in the formation of a fully-formed chick.

Steps of chick embryo development:

In the process of chick embryo development there are overall 6 steps:

1. Fertilization:

• Fertilization is the union of sperm and egg cells, resulting in the formation of a zygote.
• In the chick, fertilization occurs in the upper oviduct, where sperm are stored after being ejaculated into the cloaca of the hen.
• The egg is surrounded by a thick, protective shell, which is permeable to gases but not to water.

3. Cleavage:

• Cleavage is the series of mitotic divisions that occur in the zygote, resulting in the formation of a ball of cells called a blastoderm.
• In the chick, cleavage is rapid and asynchronous, resulting in a blastoderm of around 128 cells by the end of the first day of development.
• The blastoderm is arranged in a single layer, called the blastodermic vesicle, around a fluid-filled central cavity called the blastocoele.

3. Gastrulation:

• Gastrulation is the process by which the blastodermic vesicle is transformed into a three-layered embryo, consisting of the endoderm, mesoderm, and ectoderm.
• In the chick, gastrulation begins on the second day of development and is characterized by the formation of a primitive streak, which marks the site of ingression of cells from the epiblast to form the three germ layers.
• The endoderm forms the lining of the gut and gives rise to the respiratory and digestive systems, the mesoderm forms the muscles, skeleton, and blood vessels, and the ectoderm forms the epidermis and nervous system.

4. Neurulation:

• Neurulation is the process by which the ectoderm gives rise to the nervous system.
• In the chick, neurulation begins on the third day of development and is characterized by the formation of a neural plate, which folds to form a neural tube.
• The neural tube eventually gives rise to the brain and spinal cord.

5. Organogenesis:

• Organogenesis is the process by which the three germ layers give rise to the various organs and structures of the body.
• In the chick, organogenesis begins on the fourth day of development and continues throughout the remaining period of development.
• During organogenesis, the heart, blood vessels, somites, limb buds, and other structures begin to form.

6. Hatching:

• Hatching is the process by which the fully-formed chick emerges from the egg.
• In the chick, hatching occurs on the 21st day of development. It is triggered by the chick’s own activity, such as pecking at the shell. In addition to this decreasing oxygen and increasing carbon dioxide levels inside the egg also occurs.
• After hatching, the chick is able to move around and feed independently.

Conclusion:

Chick embryo development is a complex process that involves a series of morphological changes, beginning with fertilization and culminating in the formation of a fully-formed chick.

Chick embryos are a widely used model organism for studying development due to their accessibility and similarity to human development. This allows scientists to gain insight into the mechanisms of development and develop new strategies for treating developmental disorders.