First meiotic division of primary oocytes completes in the -

The correct answer is Option (2) → Tertiary follicle

In oogenesis, each primary oocyte starts meiosis in the fetal ovary and stops in prophase I. It finishes the first meiotic division only much later, inside the tertiary follicle, giving a large secondary oocyte and a tiny first polar body. Q43 of this paper asks the same point.

Option (1) Fetal ovary — Incorrect. The first meiotic division starts in the fetal ovary, but it is stopped there and does not finish.

Option (2) Tertiary follicle — Correct. The division is completed in the tertiary follicle, the follicle with the fluid-filled antrum.

Option (3) Graafian follicle — Incorrect. By the time the tertiary follicle becomes a Graafian follicle, the first division is already over. The Graafian follicle holds the secondary oocyte.

Option (4) Before puberty — Incorrect. Before puberty the primary oocytes stay stopped in prophase I. Follicles grow and complete the division only after puberty.

NCERT Extract:
Gametogenesis – “… The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles. The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum. The theca layer is organised into an inner theca interna and an outer theca externa. It is important to draw your attention that it is at this stage that the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body (Figure 2.8b).”

Figure 2.8 Schematic representation of (a) Spermatogenesis; (b) Oogenesis