Why mammalian RBC does not have nucleus in it?

Answer 1

Mammal RBC's do have nuclei in them in their early stages, but by the time they reach maturity the nucleus is gone. There is no need for the nucleus after maturity since the cell's function is fairly passive. A nucleus would be required if the cell needed to produce a product or perform a task like cell division, but since it doesn't need to do these things a nucleus is not necessary. The nucleus is required at the early stages in order to produce the hemoglobin that eventually fills the cell. If the nucleus didn't disappear it would either make the cell too large to slip through capillaries or would reduce the oxygen carrying ability of the cell by displacing some of the hemoglobin that would fill it.

Answer 2

Mammalian red blood cells (RBCs) do not have a nucleus because the absence of a nucleus allows them to contain more hemoglobin, which is essential for their main function of transporting oxygen. The lack of a nucleus also gives RBCs their biconcave shape, allowing them to efficiently carry oxygen and pass through capillaries. The absence of a nucleus in RBCs also ensures a larger surface area for gas exchange.