 An <unk> cell contains no nucleus and is , therefore , incapable of dividing to produce daughter cells . The best @-@ known <unk> cell is the mammalian red blood cell , or <unk> , which also lacks other organelles such as mitochondria , and serves primarily as a transport vessel to ferry oxygen from the lungs to the body 's tissues . <unk> mature through <unk> in the bone marrow , where they lose their nuclei , organelles , and ribosomes . The nucleus is expelled during the process of differentiation from an <unk> to a <unk> , which is the immediate precursor of the mature <unk> . The presence of <unk> may induce the release of some immature " <unk> " <unk> into the bloodstream . <unk> cells can also arise from flawed cell division in which one daughter lacks a nucleus and the other has two nuclei . 
