Question: How does one define a spermatogonium? Answer: Spermatogonium is the term given to a relatively unspecialized diploid germ cell present in the seminiferous epithelium after the start of spermatogenesis that is able to carry out mitotic divisions, ultimately giving rise to primary spermatocytes.

Question: Is there more than 1 type of spermatogonia?

Answer: Yes, there are a number of spermatogonial types. Unfortunately, although the first assigned names were logical to those who conceived of them, the detection of more spermatogonial cell types has made the nomenclature rather confusing. The following questions should help clarify this.

Question: How are spermatogonia named? Answer: In the beginning only 2 types of spermatogonia were described. The first, type A spermatogonium, did not display heterochromatin in the nucleus and the second, type B spermatogonium, did display heterochromatin (Figure 1). Shortly thereafter, someone found a type of spermatogonium that had an intermediate amount of heterochromatin, which was termed intermediate (In) spermatogonium. These names are historical, and they are broad categories of cells. When more generations of spermatogonia were discovered, especially among the type A category, new names were devised to categorize them.

Question: It was the amount of heterochromatin that cells possessed that allowed them to be initially categorized?