It happens when similar environments produce similar adaptations in organisms of every different ancestry; the adaptations were not inherited form of a common ancestor. It is th evolution of outwards similarities in organisms are not closely related.The resemblance of unrelated species is caused by natural selection in convergent evolution.
The nucleus is the largest and the heavies part of the eukaryotic cell and contains nucleic acids. Due to its high density and size, it is the easiest part that can be seen within cell.
Nucleus is said to be the commander in chief in protein production. It is where the generic material called the DNA or Deoxyribonucleic acid is stored. DNA is a large molecule which commands the other parts for cell duplication and protein building. It is made up of small units called the base. The four bases that made up the DNA are; Adenine, Cytosine, guanine and thymine.