which of the following is correct regarding cleavage division?

Options

A. cleavage divisions are resulting in formation of blastomeres
B. cleavage divisions in mammals are slow and synchronous
C. during cleavage there is increase in DNA :cytoplasm ratio
D. zona pellucida breaks after 3rd cleavage division

Answer

To answer the question regarding which of the following statements is correct about cleavage division, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Cleavage Division**:
- Cleavage division refers to the series of rapid mitotic divisions that occur after fertilization, leading to the formation of a multicellular structure from a single-celled zygote.

2. **Analyzing the First Statement**:
- The first statement claims that cleavage divisions result in the formation of blastomers.
- **Evaluation**: This statement is correct. Blastomers are indeed the cells produced as a result of cleavage divisions of the zygote.

3. **Analyzing the Second Statement**:
- The second statement states that cleavage division in mammals is slow and asynchronous.
- **Evaluation**: This statement is also correct. In mammals, cleavage divisions are slower compared to other organisms and do not occur simultaneously, hence they are asynchronous.

4. **Analyzing the Third Statement**:
- The third statement mentions that during cleavage, there is an increase in the DNA and cytoplasmic ratio.
- **Evaluation**: This statement is incorrect. During cleavage, the overall size of the embryo does not increase significantly, and the cytoplasmic volume remains relatively constant while the number of nuclei increases, leading to a decrease in the nuclear-to-cytoplasmic ratio.

5. **Analyzing the Fourth Statement**:
- The fourth statement claims that the Zona Pellucida breaks after the 3rd cleavage division.
- **Evaluation**: This statement is incorrect. The Zona Pellucida is broken down when the sperm fertilizes the ovum, not specifically after the third cleavage division.

### Conclusion:
Based on the evaluations, the correct statements regarding cleavage division are the first and second statements.

### Final Answer:
- The correct statements regarding cleavage division are:
1. Cleavage divisions result in the formation of blastomers.
2. Cleavage division in mammals is slow and asynchronous.