There is no way that a spermatogonium will ever be able to differentiate into a liver cell for instance. However, the germ cells contain the potential to be transmitted to the next generation and contribute one half of the DNA of the next individual. Under the influence of the surrounding somatic component of the testis or ovary the germ cells multiply by successive mitotic divisions. In the male this process continues throughout life but in females it stops prior to birth. Meiosis The reduction in chromosome number from diploid to haploid is accomplished by the specialised cell divisions of meiosis .
Cells prepare for meiosis by replication of their genetic material as for mitosis.
The chromosomes first become visible as thin threads within the nucleus at the stage called leptotene . In the next phase, zygotene , the homologous pairs of chromosomes become closely associated along their lengths by a process called synapsis to form a structure comprised of two chromosomes, a bivalent . The bivalents shorten and thicken throughout the next stage pachytene , synapsis is complete and the bivalents are held together throughout their length by a structure known as the synaptonemal complex . The chromosomes continue to condense and the synaptonemal complex breaks down. The homologous chromosomes appear to repel each other and remain held together only at chiasmata , the points where crossing over have occured, and at the centromere.