Red blood cells in mammals anucleate when mature, meaning that they lack a cell nucleus. In comparison, the red blood cells of other vertebrates have nuclei the only known exceptions are salamanders of the genus batrachoseps and fish of the genus maurolicus. In the mature form, red blood cells, or erythrocytes, do not have nuclei however, they have not always been without nuclei. An intermediate form of red blood cells, called a normoblast, expels its nuclei as the amount of hemoglobin accumulates in the developing blood cell. Mature red blood cells do not need to have a nucleus because they have already made all the proteins they will ever need. When red blood cells (erythrocytes) are produced in the bone marrow, they initially do contain a nucleus. In maturation the cell will extrude its nucleus, a process called enucleation. When the red blood cells enter circulation, they dont have a nucleus. The lack of a nucleus is an adaptation of the cell to be better equipped for its task. Mammalian red blood cells have a nucleus initially, but do not have one once mature. immature red blood cells actually do have a nucleus but when they differentiate to become the mature red blood cells the nucleus is actually ejected, so they have no nucleus and no dna. As to why this is and how they function, i think the answer is really lies in what they do. Red blood cells, their only real job is to carry oxygen around the body. Red cells do not have a nucleus, as this is lost during formation. In paraffin-processed tissue sections, red cells appear smaller and the biconcave shape is generally not discernible. Ultrastructurally, red cells have a cell membrane which surrounds an electron-dense cytoplasm that contains haemoglobin. Mature red blood cells (rbcs) do not possess nucleus along with other cell organelles such as mitochondria, golgi apparatus and endoplasmic reticulum in order to accommodate greater amount of. Red blood cells, or erythrocytes (erythro red cyte cell), are specialized cells that circulate through the body delivering oxygen to cells they are formed from stem cells in the bone marrow. In mammals, red blood cells are small biconcave cells that at maturity do not contain a nucleus or mitochondria and are only 78 m in size.