Bead-like thickened portions of leptotene chromosomes are

Options

A. Puffs
B. Chromomeres
C. Centromeres
D. Genes

Answer

**Step-by-Step Solution:**

1. **Understanding the Leptotene Stage**: The leptotene stage is the first substage of prophase I in meiosis, where chromosomes begin to condense and become visible. Each chromosome consists of two sister chromatids.

2. **Chromatin Condensation**: During the leptotene stage, the diffuse chromatin condenses into long, thin strands. This process makes the chromosomes more visible under a microscope.

3. **Identifying Bead-like Structures**: As the chromosomes condense, they exhibit bead-like thickened portions. These structures are important for understanding the organization of the chromosome.

4. **Terminology**: The bead-like thickened portions of the leptotene chromosomes are specifically referred to as "chromomers." This term is used to describe the localized areas of condensation along the chromosome.

5. **Eliminating Incorrect Options**:
- **Puffs**: These are features of polytene chromosomes and are not found in leptotene chromosomes.
- **Centromeres**: These are the constricted regions of chromosomes that separate the short arm (P arm) from the long arm (Q arm) but do not refer to the bead-like structures.
- **Genes**: While genes are segments of DNA, they do not describe the bead-like thickened portions.

6. **Conclusion**: The correct answer to the question is "Chromomers," as they accurately describe the bead-like thickened portions of leptotene chromosomes.

**Final Answer**: The bead-like thickened portions of leptotene chromosomes are called "Chromomers."

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