Question

If RBCs don't have a nucleus then how do they divide in the bone marrow?

Answer 1

Hint: The nucleus is a membrane-bound organelle that contains eukaryotic organisms' genetic material (DNA). As such, it contributes to cell integrity by facilitating transcription and replication processes. It is the largest organelle inside the cell, accounting for roughly one-tenth of the total cell volume.

Complete answer:
Erythrocytes, also known as Red Blood Cells (RBCs), are an important cellular component of blood. These cells circulate in the blood, carrying oxygen from the lungs to all of the body's tissues. It is responsible for giving blood its distinctive color. Human mature erythrocytes are rounded, small, and biconcave, resembling dumbbells. Because the cell is malleable, it can reform to take up a bell shape when it passes through the super tiny blood vessels.
RBCs, also known as erythrocytes, have a diameter of 7-8 m and an unusual structure in comparison to most other human body cells. These cells resemble a donut because they are biconcave, with a thicker periphery than a thinner center. Because they are lost during erythropoiesis, these cells are anuclear and lack any other intracellular organelles. There are two major structures: cytoplasm engirdled by a cell membrane.
Red blood cells have adapted this feature (no nucleus) for a variety of reasons. It simply allows more hemoglobin to be carried by the red blood cell. The absence of a nucleus in RBC allows the cell to have a distinct biconcave shape, which aids in diffusion. Mature red blood cells lack DNA and are unable to synthesize RNA.

Note:
Red blood cells are normally synthesized in the bone marrow. They have a lifespan of about 120 days before dying. The primary function of these red cells and their hemoglobin is to transport oxygen from the gills/lungs to all tissues of the body, as well as carbon dioxide (a byproduct of metabolism) to the lungs for exhalation.