Question

In an egg, the type of cleavage is determined by

• A. the amount and distribution of yolk
• B. the number of egg membranes
• C. the shape and size of the sperm
• D. the size and location of the nucleus.

Answer 1

The Correct Option is A

The type of cleavage in an egg is primarily determined by the amount and distribution of yolk within the egg. This is due to the following reasons:

1. Role of Yolk: The yolk provides nutrients to the developing embryo. The amount of yolk can influence where and how cleavage occurs. For example:
   • Holoblastic Cleavage: This occurs in eggs with a small amount of yolk uniformly distributed, such as those of amphibians. This results in the complete division of the egg.
   • Meroblastic Cleavage: This occurs in eggs with a large amount of yolk, such as those of birds. The division is partial because the yolk impedes the cleavage furrows.
2. Distribution of Yolk: The cleavage pattern can also change based on whether the yolk is concentrated at one end (telolecithal eggs) or evenly distributed (isolecithal eggs).

Now, let's evaluate the given options:

1. The amount and distribution of yolk: Correct, as explained above, the yolk's amount and placement dictate the cleavage pattern.
2. The number of egg membranes: Incorrect. Egg membranes do not directly affect cleavage patterns.
3. The shape and size of the sperm: Incorrect. The sperm's attributes determine fertilization success but not the cleavage pattern.
4. The size and location of the nucleus: Incorrect. While the nucleus's activity is crucial for cell division, it is not a determining factor for cleavage type.

In conclusion, the correct answer is indeed the amount and distribution of yolk, as it directly impacts how the egg divides during early embryonic development.