Which type of sperm maintains a supply of undifferentiated cells?

Type A sperm, also referred to as Type A spermatogonia, is responsible for maintaining a reservoir of undifferentiated cells in the male germline. These cells can divide and differentiate into the various types of sperm cells needed for reproduction. Type A spermatogonia undergo mitosis to produce more Type A and Type B cells. While Type B spermatogonia will eventually differentiate into primary spermatocytes that initiate the process of meiosis, Type A cells are crucial for sustaining the population of stem cells, ensuring that there is a continuous supply available for spermatogenesis.

In contrast, the other types mentioned, such as Type B, C, and D, play distinct roles in the maturation and differentiation of sperm but do not maintain the pool of undifferentiated stem cells. This differentiation process is vital for producing functional sperm, but without Type A spermatogonia, there would be no ongoing replenishment of the stem cell population necessary for ongoing sperm production.