Practice question

Symmetric self-renewing division produces two daughters both retaining stem character, full self-renewal transcriptional program, and niche responsiveness, thereby increasing absolute stem cell number inside tissue. This mode dominates during development to rapidly expand progenitor pools, during wound healing to repopulate emptied niches, and in culture systems where niche constraints are experimentally relaxed. Mechanistically, mitotic spindle orientation parallel to niche basement membrane places both daughters within Wnt-rich microenvironment, preserving expression of Lgr5 and other stem markers. Conversely asymmetric division maintains constant numbers, while symmetric differentiating divisions generate two committed cells causing contraction.