Embryology: Types of Eggs

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Questions and Answers

What is the main influence of yolk on cleavage?

It affects only the rate of cleavage.

It impacts both the rate and pattern of cleavage. (correct)

It solely determines the number of cells formed.

It determines the size of blastomeres only.

What characterizes determinate cleavage?

All blastomeres can become a complete organism.

Only some cells have the capacity to divide.

The developmental fate of cells is predetermined early. (correct)

Each cleavage division results in equal-sized cells.

Which plane of cleavage runs through the animal-vegetal axis and bisects the egg?

Latitudinal plane

Vertical plane

Equatorial plane

Meridional plane (correct)

In which type of cleavage do only a portion of the egg's cells divide?

Meroblastic cleavage Signup and view all the answers

What occurs during equal holoblastic cleavage?

Blastomeres are approximately equal in size. Signup and view all the answers

Which type of cleavage typically occurs in reptiles and birds?

Discoidal meroblastic cleavage Signup and view all the answers

What is a characteristic of indeterminate cleavage?

Each blastomere can develop into a whole organism. Signup and view all the answers

Which cleavage pattern produces macromeres and micromeres due to yolk concentration?

Unequal holoblastic cleavage Signup and view all the answers

What is the main role of yolk in animal eggs?

To nourish the embryo during development Signup and view all the answers

Which type of egg has no yolk particles?

Alecithal type Signup and view all the answers

In which type of egg are yolk particles concentrated at one end of the egg?

Telolecithal type Signup and view all the answers

What occurs immediately after fertilization of an egg?

Zygote formation Signup and view all the answers

What refers to the initial mitotic divisions of the fertilized egg?

Cleavage Signup and view all the answers

Which axis of the egg has the highest concentration of yolk?

Vegetal pole Signup and view all the answers

How are the cells produced from cleavage referred to?

Blastomeres Signup and view all the answers

What does the cleavage furrow signify in the cleavage process?

Initiation of the cleavage process Signup and view all the answers

Study Notes

Embryology: Types of Eggs

Animal eggs contain nutrients (protein, lipid, glycogen) to nourish the embryo, collectively called yolk.
Yolk proteins are produced in the liver (vertebrates) or fat bodies (insects).
Eggs are classified by yolk presence/absence and quantity:

Classification by Yolk Amount

Alecithal: No yolk, found in placental mammals.
Oligolecithal: Small amount of yolk, found in Echinoderms and Amphioxus.
Mesolecithal: Moderate amount of yolk, found in toads.
Macrolecithal: Large amount of yolk, found in many species.

Classification by Yolk Distribution

Isolecithal: Yolk distributed evenly throughout the cytoplasm, found in fishes.
Centrolecithal: Yolk concentrated in the center of the egg, found in insects and arthropods.
Telolecithal: Yolk concentrated at one end (pole) of the egg, found in some fishes and toads.

Zygote Formation

A fertilized egg (zygote) develops into an embryo after the first cleavage (division).
The zygote forms a diploid multicellular organism via repeated mitotic divisions and cellular differentiation.

Cleavage

Cleavage is the initial mitotic divisions in a fertilized egg.
The pole with most yolk is called the vegetal pole, the opposite the animal pole.
Cleavage initiates by furrows (grooves) that start at a single point on the egg.
A cleavage furrow forms and deepens, eventually separating the egg into blastomeres.

Yolk Influence on Cleavage

Yolk affects cleavage rate and pattern.
Determinate cleavage: The fate of cells is determined early in development; each blastomere may not form a whole embryo.
Indeterminate cleavage: Each blastomere can develop into a complete organism.

Planes of Cleavage

Cleavage occurs in specific planes:
- Meridional: Passes through the animal-vegetal axis, bisecting both poles.
- Vertical: Passes from the animal to vegetal pole, not through the egg's center.
- Equatorial: Passes at right angles to the main axis, at the midpoint between animal and vegetal poles.
- Latitudinal/horizontal: Similar to equatorial but courses through the cytoplasm on either side.

Types of Cleavage Patterns

Holoblastic: Complete divisions of the egg.
- Equal holoblastic: Blastomeres are roughly equal in size.
- Unequal holoblastic: Blastomeres uneven in size due to yolk concentration.
Meroblastic: Partial divisions, where only part of the egg divides.
- Discoidal meroblastic: A disc-shaped region of the egg (blastodisc) divides, while the yolk remains undivided. Found in reptiles and birds.
- Superficial meroblastic: Nuclei migrate to the periphery, and cleavage occurs only in the peripheral cytoplasm. Found in insects.

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Description

Explore the fascinating world of embryology with this quiz on the different types of eggs based on yolk presence, amount, and distribution. Learn about alecithal, oligolecithal, mesolecithal, and macrolecithal eggs, as well as their developmental significance in various species.