Practice question

Totipotency denotes ability to generate complete organism including embryonic and extraembryonic tissues. While mammalian totipotency is limited to zygote and early blastomeres up to eight-cell stage, certain lower metazoans retain organism-wide cellular plasticity. Hydra, a cnidarian, contains interstitial stem cells distributed throughout body that remain totipotent, capable of forming ectoderm, endoderm, nematocytes, neurons, and germ cells. Each fragment containing interstitial cells can regenerate entire animal. Mice, Drosophila, and zebrafish show lineage-restricted somatic cells early, so individual differentiated cells cannot regenerate whole organisms spontaneously.