In human which of the following has 23 chromosomes ?

Question

Accepted Answer

The correct option is 2: Secondary oocyte

The secondary oocyte is the correct answer because it is a **haploid (n)** cell, which means it contains only a single set of chromosomes, and in humans, this number is precisely **23 chromosomes**. This is achieved during oogenesis, the process of female gamete formation. The secondary oocyte is formed when the diploid (2n) **primary oocyte** completes the first meiotic division (Meiosis I). Meiosis I is a crucial reductional division that halves the total number of chromosomes from 46 to 23, separating homologous chromosomes. This cell is an arrested gamete, pausing its development at metaphase II of Meiosis II. It is in this haploid, arrested state that the cell is released from the ovary during ovulation, prepared to be fertilized.

The incorrect option is 1: Spermatogonia

Spermatogonia are the male germ cells, or stem cells, found on the inner wall of the seminiferous tubules of the testes. As undifferentiated, precursor cells, their primary role is to multiply via **mitosis** to continuously replenish the germline. Mitosis is an equational division, meaning the daughter cells must maintain the chromosome number of the parent cell. Therefore, spermatogonia are **diploid (2n)** cells, and each one contains the full complement of **46 chromosomes**. Only when a spermatogonium differentiates into a primary spermatocyte and begins the meiotic process does the chromosome number change.

The incorrect option is 3: Zygote

The zygote is the single cell formed immediately following **fertilization**, which is the union of the male gamete (sperm) and the female gamete (ovum). The fundamental purpose of fertilization is to restore the diploid state, marking the beginning of the new organism. Since a haploid sperm (23 chromosomes) fuses with a haploid ovum (23 chromosomes), the resulting zygote is **diploid (2n)**. Therefore, a human zygote possesses the full, species-specific chromosome count of **46 chromosomes**.

The incorrect option is 4: Oogonia

Oogonia are the primordial germ cells in the female reproductive system that undergo rapid multiplication during **fetal development**. They are the progenitor cells for all future female gametes. Like spermatogonia, oogonia divide exclusively by **mitosis** to increase their population size before the reductional meiotic divisions begin. Consequently, oogonia are **diploid (2n)** cells and contain **46 chromosomes**. Once they cease mitotic division, they enlarge and differentiate into the primary oocytes, which still possess the diploid number until Meiosis I is completed.