Practice question

If differentiation caused permanent gene deletion, differentiated cells could not generate entire organism. Cloning experiments overturn this idea by demonstrating nucleus from specialized cell retains complete genome. Transfer of intestinal cell nucleus in frogs by Gurdon and mammary cell nucleus in sheep by Wilmut yielded fertile adults, proving genetic totipotency persists despite cellular specialization. Morphogenesis, organogenesis, and fertilization do not directly test genome retention; they illustrate patterning processes. Cloning thus provides functional proof that phenotype differences arise from gene regulation, not gene loss, supporting equivalence principle central to epigenetics.