What cell in the body doesn't have a nucleus when it is mature?

Red Blood Cells (erythrocytes) don't have nuclie when they are mature, the same thing applies to platelets (thrombocytes).

Answer

^correct red blood cells are full of hemoglobin wich caries oxygen

Answer

First answer is spot-on.

Corralaries: 1. You can't clone a human being from a red blood cell. (Even if we knew how to clone human beings :) )2. You can't do genetic test that depend on the genome using a red blood cell. (You can do genetic test based on microsomal RNA since the microsomes are intact and weren't part of the cell's nucleus to begin with.)