How many meiotic divisions have to occur for a spermatogonium to produce 64 haploid sperm cells?
Answers
Spermatocytes
Spermatocytes are formed from the final mitotic division of the type B spermatogonia. The cells then undergo meiosis, passing through preleptotene, leptotene, zygotene, pachytene, and diplotene stages, diakinesis, and the first meiotic division to produce secondary spermatocytes. The second meiotic division follows rapidly to produce the haploid spermatid. As the spermatocytes pass through meiotic prophase they become larger and the appearance of the nuclear chromatin alters, reflecting the condensation and movement of the chromosomes as they prepare for meiotic division. Preleptotene spermatocytes produced by the dividing B spermatogonia are almost identical to their parent cell, but have a slightly smaller nucleus. During preleptotene, DNA synthesis occurs and the cells move away from the basement membrane and pass through the tight junctional complex between the Sertoli cells. During leptotene, the chromosomes condense to form thin delicate filaments, coming together in zygotene as homologous pairs that form characteristic tripartite structures in the nucleus called synaptonemal complexes (Figure 18.4). During the pachytene phase, the chromosomes become shorter and thicker and split into two chromatids joined by the centromere. Pachytene is a lengthy phase, lasting about 12 days in the rat; during this time there is a marked increase in cellular and nuclear volume. As the cells enter diplotene and diakinesis, the chromosomes begin to separate and condense further while synaptonemal complexes disappear. Diakinesis and the two meiotic divisions occur in rapid succession; a single cross section of tubule will often contain diakinetic spermatocytes, spermatocytes in the first and second stages of division, secondary spermatocytes (from the first division), and the newly formed spermatids from the second division.