Question

types of egg and cleavage pettern​

Answer 1

Answer:

radial, spiral, bilateral, and rotational. Egg cells that have larger quantities of yolk undergo meroblastic cleavage after fertilization, in which only a portion of the zygote undergoes cleavage. ... Such eggs display holoblastic cleavage patterns

Answer 2

Answer:

Cleavage Patterns And Morphogenesis

A fertilized zygote undergoes series of mitotic divisions known as cleavage, which results in the formation of multicellular embryo. Cleavage, also known as cellulation, continues repeatedly until these divisions result in blastomere. The blastomere then continues developing into specialized regions, and differentiates into various cell types that constitute the organism as a whole.

Cleavage is specific to species and is dependent primarily on two factors:

• Quantity of yolk protein and its distribution within the cytoplasm

• Factors in the cytoplasm that impact the time of mitotic spindle formation and its angle

In organisms that produce eggs with little yolk, the zygote divides by holoblastic cleavage. In such cleavages, the entire cell is divided equally. Four major holoblastic cleavage types can be observed in general: radial, spiral, bilateral, and rotational. Egg cells that have larger quantities of yolk undergo meroblastic cleavage after fertilization, in which only a portion of the zygote undergoes cleavage. Three major meroblastic cleavage types are: bilateral, discoidal, and superficial.

Eggs are classified based on the amount and distribution of yolks into the following types.

1. Isolecithal eggs have sparse amounts of yolk but it is evenly distributed throughout the egg. Such eggs display holoblastic cleavage patterns. The cleavage groove spreads evenly around the egg. Examples are eggs of sea urchin and mouse.

2. Mesolecithal eggs have intermediate amounts of yolk, which is often unevenly distributed in the egg. Examples are eggs of frogs.

3. Telolecithal eggs have thick yolk, but they are located in one end of the egg. In such eggs, cell division occurs only in the area that is filled with cytoplasm. Such eggs display a discoidal pattern of cleavage. Examples are eggs of birds and reptiles.

4. Centrolecithal eggs have yolks located in the center of the egg. Such eggs display superficial cleavage with divisions occurring on the surface of the egg. An example is egg of a fly.

Four major holoblastic cleavage types can be observed in the absence of a large amount of yolk: radial, spiral, bilateral, and rotational.

Morphogenesis

Cell shape changes and movements are primary to early development as the embryo needs to change itself from a simple ball or sheet of cells into a multilayered structure. These highly coordinated changes and rearrangements in cells occur during gastrulation. Cells that eventually form the endodermal and mesodermal organs move toward the inside of the embryo, and the cells that are destined to become skin and nervous tissue spread out around the embryo. Gastrulation comprises of various cell movements like invagination, ingression, involution, delamination, and epiboly.

Another important event in embryonic development is the formation of embryonic axes. (anteroposterior axis, dorsoventral axis, and right-left axis)