Meiosis-I is reductional division while meiosis-ll is equational division.

Reductional division during oogenesis starts in:

The correct answer is option 'B', which states that reductional division during oogenesis starts in the primary oocyte within the primary follicle.

Explanation:

Oogenesis is the process of the formation and development of female gametes, or eggs. It occurs in the ovaries and involves several stages of cell division and maturation. Reductional division is a crucial step in oogenesis that leads to the formation of haploid gametes.

Here is a detailed explanation of the stages of oogenesis and where reductional division starts:

1. Primordial follicle stage:
- Oogenesis begins during fetal development when primordial germ cells in the ovaries differentiate into oogonia.
- Each oogonium undergoes mitosis to produce a primary oocyte.

2. Primary follicle stage:
- Primary oocytes are surrounded by a layer of granulosa cells, forming a primary follicle.
- However, the primary oocytes are arrested in the prophase stage of the first meiotic division, known as the dictyate stage, until puberty.

3. Secondary follicle stage:
- At puberty, a few primary follicles are selected to continue development under the influence of follicle-stimulating hormone (FSH).
- The primary oocyte within the selected follicle starts to grow, and the surrounding granulosa cells proliferate.
- The primary oocyte completes the first meiotic division, resulting in the formation of two haploid cells: a secondary oocyte and a polar body.
- The secondary oocyte receives most of the cytoplasm, while the polar body, which contains half of the chromosomes, is smaller and eventually degenerates.

4. Graafian follicle stage:
- The secondary oocyte, now arrested in the metaphase stage of the second meiotic division, is released from the ovary during ovulation.
- If fertilization occurs, the secondary oocyte will complete the second meiotic division, resulting in the formation of a mature egg and another polar body.
- If fertilization does not occur, the secondary oocyte degenerates.

Therefore, reductional division during oogenesis starts in the primary oocyte within the primary follicle. This division results in the formation of haploid cells, the secondary oocyte, and the polar body.