In human reproduction, by which type of cell division are haploid gametes (sperm and ova) produced from diploid germ cells?

Introduction / Context:
Human beings and many other organisms reproduce sexually, which requires specialized cells called gametes. Gametes contain half the usual number of chromosomes so that when they fuse during fertilization, the normal diploid number is restored. This question asks which type of cell division produces these haploid gametes from diploid germ cells.

Given Data / Assumptions:
- Somatic cells in humans are diploid, with two sets of chromosomes.
- Gametes are haploid, with one set of chromosomes.
- Mitosis and meiosis are two different forms of nuclear division.

Concept / Approach:
Mitosis produces two genetically identical diploid daughter cells and is used for growth, repair, and asexual reproduction. Meiosis, in contrast, involves two successive divisions, meiosis I and meiosis II, and produces four haploid cells from one diploid parent cell. Meiosis includes processes such as crossing over and independent assortment, which generate genetic variation among gametes. In humans, meiosis occurs in the testes and ovaries to produce sperm and eggs.

Step-by-Step Solution:
Step 1: Recall that gametes must be haploid so that when they fuse at fertilization, the resulting zygote is diploid. Step 2: Recognize that mitosis conserves chromosome number, so diploid cells remain diploid after mitotic division. Step 3: Understand that meiosis reduces chromosome number by half, producing haploid cells. Step 4: Note that meiosis also introduces genetic variation through crossing over and independent assortment. Step 5: Conclude that meiosis is the type of division that produces human gametes.

Verification / Alternative check:
Biology texts describe spermatogenesis and oogenesis as processes that include meiosis to form haploid sperm and eggs. Diagrams show a diploid germ cell undergoing meiosis I and meiosis II to form four haploid cells, confirming the role of meiosis in gamete production.

Why Other Options Are Wrong:
Option A: Mitosis produces genetically identical diploid cells and does not reduce chromosome number, so it cannot produce haploid gametes.
Option C: Replication without division would increase DNA content but not create separate cells and is not a real pathway for producing gametes.
Option D: This is incorrect because meiosis is clearly involved in the production of human gametes.

Common Pitfalls:
Some learners confuse mitosis and meiosis because both involve stages like prophase, metaphase, anaphase, and telophase. A useful memory aid is that mitosis maintains chromosome number and meiosis makes gametes. Association of the prefix mei with the idea of reduction can help remember that meiosis reduces chromosome number.

Final Answer:
The correct answer is meiosis, a two stage division that produces haploid cells with genetic variation because meiosis is the specialized cell division that forms human gametes from diploid germ cells.