Have 46 chromosomes, whereas have 23. Spermatids; spermatozoa Secondary spermatocytes; primary spermatocytes Spermatogonia; primary spermatocytes Type A spermatogonia; type B spermatogonia Primary spermatocytes; spermatids
The correct answer and explanation is:
Correct Answer: Primary spermatocytes; spermatids
Explanation (300 words):
Human cells typically contain 46 chromosomes (23 pairs). However, during the production of gametes (sperm and egg cells), a special type of cell division called meiosis occurs. Meiosis reduces the chromosome number by half, ensuring that when a sperm and egg unite during fertilization, the resulting zygote has the correct number (46).
In spermatogenesis (the process by which sperm are formed in males), the following sequence occurs:
- Spermatogonia are the diploid (2n) stem cells located in the seminiferous tubules of the testes. These cells have 46 chromosomes.
- Some spermatogonia differentiate into primary spermatocytes, which are also diploid (46 chromosomes).
- Primary spermatocytes undergo meiosis I, a reduction division, forming two secondary spermatocytes, each with 23 chromosomes but still duplicated chromatids.
- Secondary spermatocytes quickly enter meiosis II, leading to the formation of spermatids, which are haploid (23 chromosomes) and have a single chromatid per chromosome.
- Spermatids mature into spermatozoa (sperm cells) without further division, still containing 23 chromosomes.
So, to answer the question:
- Primary spermatocytes start with 46 chromosomes, the full diploid set.
- After meiosis, spermatids have 23 chromosomes, making them haploid.
This reduction is crucial for maintaining genetic stability across generations. If gametes carried 46 chromosomes, fertilization would result in zygotes with 92 chromosomes, which would be fatal or lead to major abnormalities.
Thus, “Primary spermatocytes; spermatids” correctly identifies the stage where cells go from diploid (46 chromosomes) to haploid (23 chromosomes), matching the key transition in human spermatogenesis.