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The blastodisc, also called the germinal disc, is the embryo-forming part on the yolk of the egg of an animal that undergoes discoidal meroblastic cleavage. Discoidal cleavage occurs in those animals with a large proportion of yolk in their eggs, and include insects, fish, reptiles and birds.
The germinal disc is a white plaque (three to four mm in diameter) on the top of the oocyte and occupies about 1% of cell volume. It contains the nucleus and 99% of cytoplasmic organelles such as elongated membrane-bound vesicles, mitochondria, and glycogen granules.
The yolk is the source of food for the embryo and contains all the fat in the egg. The small white spot on the yolk is call the germinal disc. The germinal disc is where the female's genetic material is found.
A blastoderm (germinal disc, blastodisc) is a single layer of embryonic epithelial tissue that makes up the blastula. It encloses the fluid filled blastocoel. Gastrulation follows blastoderm formation, where the tips of the blastoderm begins the formation of the ectoderm, mesoderm, and endoderm.
A small, almost unnoticeable white dot on the yolk of an egg is called the germinal disc. It's the entrance to a tiny path that leads to the center of the yolk. And it's this path that the sperm in a fertilized egg will travel to create the embryo and begin to form a baby chick.
A chick emerges from a fertile egg after twenty-one days of incubation. The germinal disc is visible on the surface of the yolk. The development of the chick begins in the single cell formed by the union of two parental cells, egg and sperm, in the process known as fertilization.
Schematic representation of parts of the germinal disc during early embryonic development; The germinal disc in upperview (A), and cross section before (B) and during (C) gastrulation.
