Questions & Answers

Cleavage found in mesolecithal egg is:
A. Holoblastic and equal.
B. Holoblastic and unequal.
C. Meroblastic.
D. Discoidal.

Answer Verified Verified
Hint: It is a rapid cell division that occurs as a fertilized egg which begins to develop into an embryo.
Eggs in embryology are classified on the basis of the quantity of yolk. Embryology is a part of biology in which we learn about prenatal gametes development, fertilization, foetus and embryos. It also includes study about congenital disorders like cleft palate, etc.

Complete answer: In order to solve this question, we need to know more about cleavage.
Cleavage: The process of the division of the ovum into smaller cells.
It is also known as embryo.
It is surrounded by the zona pellucida layer.
The morula consists of inner cell mass which are covered by the trophoblasts.
Inner cell mass gives rise to the embryoblast.
Types of cleavage are:
1. Mosaic cleavage
2. Regulative cleavage
3. Holozoic cleavage
A. Bilateral
B. Radial
C. Spiral
D. Rotational
4. Meroblastic cleavage
Mesolecithal eggs: Mesolecithal eggs are those eggs that have an intermediate size of yolk present and it is concentrated in one hemisphere.
Distribution of yolk is strongly unequal.
Examples are amphibians, eggs of shark, fishes.
Holoblastic cleavage is the complete division that means it completely penetrates the egg.
Sparse amount of yolk is present in it.
Distribution of the yolk in holozoic can be of equal or unequal type.
Holozoic and unequal types of cleavage are found in mesolecithal eggs.
Holozoic and equal amounts of cleavage are found in placental mammals.
Meroblastic cleavage: It is characterized by incomplete cleavage due to the presence of the impending mass.
Discoidal cleavage: It is a meroblastic type of cleavage in which cells are produced at the animal pole of zygote.

So, the correct option is option B holozoic and unequal.

Note: Eggs based on the quantity of yolk is:
1. Microlecithal eggs.
2. Microlecithal eggs.
3. Homolecithal eggs.
4. Telolecithal eggs.
5. Mesolecithal eggs.
6. Centrolecithal eggs.