Question

Superficial non-elastic cleavage occurs in
A) Reptiles
B) Birds
C) Mammals
D) Insects

Answer 1

To begin answering this question, we must first define cleavage. Cleavage is the division of cells in the early embryo in developmental biology. Many species' zygotes go through rapid cell cycles with no overall growth, producing a cluster of cells the same size as the original zygote.

Complete answer:
The cleavage can be holoblastic (complete or partial) or meroblastic (depending on the amount of yolk in the egg) (partial cleavage). The vegetal pole of the egg has the greatest concentration of yolk, while the animal pole has the least.

Cleavage differs from other forms of cell division in that it increases the number of cells and nuclear mass while leaving the cytoplasm alone. This means that each subdivision nearly cuts the amount of cytoplasm in each daughter cell in half, increasing the nuclear-to-cytoplasmic material ratio.

Let us analyze the give options”
Option A: Reptiles: Discoidal cleavage is common in telolecithal egg cells, monotremes, reptiles, and fish (egg cells with the yolk concentrated at one end). The "syncytial layer" refers to the layer of cells that have not fully divided and are in contact with the yolk.
Option B: Birds:Telolecithal eggs are found in birds, fish, and reptiles, whereas centrolecithal eggs are found in insects. Telolecithal eggs cleave into meroblastic discoidal strands.
Option C: Mammals:In mammals, the cells that form after cleavage are all the same size and shape. Because these eggs have less yolk in the cell, they go through Holoblastic cleavage. As a result, cleavage in mammals is Holoblastic equal.
Option D: Insects: Karyokinesis, which results in the formation of multiple nuclei but lacks cytokinesis, distinguishes superficial cleavage. With the yolk in the center, the nuclei migrate to the egg's periphery, while the plasma membrane grows inward, partitioning the nuclei into individual cells. Centrolecithal arthropods exhibit superficial cleavage (including insects).

Therefore, the correct answer is an option (D) i.e, Insects.

Note: A meroblastic cleavage in which mitosis takes place without cytokinesis, resulting in a large number of nuclei migrating to the centrolecithal egg's periphery. Add it to the mix. This type of cleavage is seen in insects that lay centrolecithal eggs (i.e., the yolk is located in the center of the egg cell).